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Title: Creation of the Teton Landscape
The Geologic Story of Grand Teton National Park
Author: J. D. Love
John C. Reed
Release Date: August 18, 2016 [EBook #52838]
Language: English
Character set encoding: UTF-8
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View west toward Grand Teton on skyline. Hedrick’s Pond surrounded
by “knob and kettle” topography is in foreground, tree-covered
Burned Ridge moraine is in middle distance, and extending from it to
foot of mountains is gray flat treeless glacial outwash plain.
_National Park Service photo by W. E. Dilley._
[Illustration: View west up Cascade Canyon, with north face of Mt.
Owen in center. _National Park Service photo by H. D. Pownall._]
_To Fritiof M. Fryxell, geologist, teacher,
writer, mountaineer, and the first ranger-naturalist
in Grand Teton National Park._
_All who love and strive to understand
the Teton landscape follow in his footsteps._
_CREATION OF THE
TETON LANDSCAPE_
The Geologic Story of
Grand Teton National Park
_By
J. D. LOVE AND JOHN C. REED, JR.
U.S. Geological Survey_
_Library of Congress Catalogue Card No._: 68-20628
_ISBN_ O-931895-08-1
1st Edition
1968
1st Revised Edition
1971
Reprinted 1979
Reprinted 1984
Reprinted 1989
Grand Teton Natural History Association
Moose, Wyoming 83012
CONTENTS
Foreword 6
THE STORY BEGINS 8
First questions, brief answers 9
An extraordinary story 10
An astronaut’s view 12
A pilot’s view 14
A motorist’s view 15
View north 15
View west 18
View south 19
A mountaineer’s view 20
CARVING THE RUGGED PEAKS 24
Steep mountain slopes—the perpetual battleground 24
Rock disintegration and gravitational movement 24
Running water cuts and carries 26
Glaciers scour and transport 28
Effects on Jackson Hole 30
MOUNTAIN UPLIFT 36
Kinds of mountains 36
Anatomy of faults 38
Time and rate of uplift 40
Why are mountains here? 41
The restless land 43
ENORMOUS TIME AND DYNAMIC EARTH 45
Framework of time 45
Rocks and relative age 45
Fossils and geologic time 46
Radioactive clocks 47
The yardstick of geologic time 48
PRECAMBRIAN ROCKS—THE CORE OF THE TETONS 51
Ancient gneisses and schists 51
Granite and pegmatite 55
Black dikes 58
Quartzite 63
A backward glance 64
The close of the Precambrian—end of the beginning 64
THE PALEOZOIC ERA—TIME OF LONG-VANISHED SEAS AND THE DEVELOPMENT
OF LIFE 66
The Paleozoic sequence 66
Alaska Basin—site of an outstanding rock and fossil record 66
Advance and retreat of Cambrian seas; an example 69
Younger Paleozoic formations 74
THE MESOZOIC—ERA OF TRANSITION 79
Colorful first Mesozoic strata 79
Drab Cretaceous strata 81
Birth of the Rocky Mountains 82
TERTIARY—TIME OF MAMMALS, MOUNTAINS, LAKES, AND VOLCANOES 86
Rise and burial of mountains 88
The first big lake 92
Development of mammals 95
Volcanoes 98
QUATERNARY—TIME OF ICE, MORE LAKES, AND CONTINUED CRUSTAL
DISTURBANCE 102
Hoback normal fault 103
Volcanic activity 103
Preglacial lakes 104
The Ice Age 105
Modern glaciers 112
THE PRESENT AND THE FUTURE 113
APPENDIX 115
Acknowledgements 115
Selected references—if you wish to read further 116
About the authors 117
Index of selected terms and features 118
_FOREWORD_
Geology is the science of the Earth—the study of the forces, processes,
and past life that not only shape our land but influence our daily lives
and our Nation’s welfare. This booklet, prepared by two members of the
U.S. Geological Survey, discusses how geologic phenomena are responsible
for the magnificent scenery of the Teton region.
Recognition of the complex geologic history of our Earth is vital to the
enjoyment and appreciation of beautiful landscapes and other natural
wonders, to the planning of our cities and highway systems, to the wise
use of our water supplies, to the study of earthquake and landslide
areas, to the never-ending search for new mineral deposits, and to the
conservation and development of our known natural resources. Who can
say, in the long run, which of the many uses of this knowledge is the
most compelling reason to seek an understanding of the Earth?
[Illustration: Signature]
W. T. Pecora, _Director_
U.S. Geological Survey
_This booklet is based on geologic investigations by the
U. S. Geological Survey in cooperation with the National Park Service,
U. S. Department of Interior._
“_Something hidden. Go and find it.
Go and look behind the Ranges—
Something lost behind the Ranges.
Lost and waiting for you. Go._”
KIPLING—_THE EXPLORER_
THE STORY BEGINS
The Teton Range is one of the most magnificent mountain ranges on the
North American Continent. Others are longer, wider, and higher, but few
can rival the breath-taking alpine grandeur of the eastern front of the
Tetons. Ridge after jagged ridge of naked rock soar upward into the
western sky, culminating in the towering cluster of peaks to which the
early French voyageurs gave the name “_les Trois Tetons_” (the three
breasts). The range hangs like a great stone wave poised to break across
the valley at its base. To the south and east are lesser mountains,
interesting and scenic but lacking the magic appeal of the Tetons.
This is a range of many moods and colors: stark and austere in morning
sun, but gold and purple and black in the softly lengthening shadows of
afternoon; somber and foreboding when the peaks wrap themselves in the
tattered clouds of an approaching storm, but tranquil and ethereal blue
and silver beneath a full moon.
These great peaks and much of the floor of the valley to the east,
_Jackson Hole_ (a _hole_ was the term used by pioneer explorers and
mountain men to describe any open valley encircled by mountains), lie
within Grand Teton National Park, protected and preserved for the
enjoyment of present and future generations. Each year more than 3
million visitors come to the park. Many pause briefly and pass on.
Others stay to explore its trails, fish its streams, study the plants
and wildlife that abound within its borders, or to savor the colorful
human history of this area.
Most visitors, whatever their interests and activities, are probably
first attracted to the park by its unsurpassed mountain scenery. The
jagged panorama of the Tetons is the backdrop to which they may turn
again and again, asking questions, seeking answers. How did the
mountains form? How long have they towered into the clouds, washed by
rain, riven by frost, swept by wind and snow? What enormous forces
brought them forth and raised them skyward? What stories are chronicled
in their rocks, what epics chiseled in the craggy visage of this
mountain landscape? Why are the Tetons different from other mountains?
First questions, brief answers
_How did the Tetons and Jackson Hole form?_ They are both tilted blocks
of the earth’s crust that behaved like two adjoining giant trapdoors
hinged so that they would swing in opposite directions. The block on the
west, which forms the Teton Range, was hinged along the Idaho-Wyoming
State line; the eastern edge was uplifted along a fault (a fracture
along which displacement has occurred). This is why the highest peaks
and steepest faces are near the east margin of the range. The hinge line
of the eastern block, which forms Jackson Hole, was in the highlands to
the east. The western edge of the block is downdropped along the fault
at the base of the Teton Range. As a consequence, the floor of Jackson
Hole tilts westward toward the Tetons (see cross section inside back
cover).
_When did the Tetons and Jackson Hole develop the spectacular scenery we
see today?_ The Tetons are the youngest of all the mountain ranges in
the Rocky Mountain chain. Most other mountains in the region are at
least 50 million years old but the Tetons are less than 10 million and
are still rising. Jackson Hole is of the same age and is still sinking.
The Teton landscape is the product of many earth processes, the most
recent of which is cutting by water and ice. Within the last 15,000
years, ice sculpturing of peaks and canyons and impounding of glacial
lakes have added finishing touches to the scenic beauty.
_Why did the Tetons rise and Jackson Hole sink?_ For thousands of years
men have wondered about the origin of mountains and their speculations
have filled many books. Two of the more popular theories are: (1)
continental drift (such as South America moving away from Africa), with
the upper lighter layer of the earth’s crust moving over the lower
denser layer and wrinkling along belts of weakness; and (2) convection
currents within the earth, caused by heat transfer, resulting in linear
zones of wrinkling, uplift, and collapse.
These concepts were developed to explain the origin of mountainous areas
hundreds or thousands of miles long but they do not answer directly the
question of why the Tetons rose and Jackson Hole sank. As is discussed
in the chapter on mountains, it is probable that semifluid rock far
below the surface of Jackson Hole flowed north into the Yellowstone
Volcanic Plateau-Absaroka Range volcanic area, perhaps taking the place
of the enormous amount of ash and lava blown out of volcanoes during the
last 50 million years. The origin of the line of weakness that marks the
Teton fault along the east face of the Teton Range may go back to some
unknown inequality in the earth’s composition several billion years ago.
Why it suddenly became active late in the earth’s history is an
unanswered question.
The ultimate source of heat and energy that caused the mountains and
basins to form probably is disintegration of radioactive materials deep
within the earth. The Tetons are a spectacular demonstration that the
enormous energy necessary to create mountains is not declining, even
though our planet is several billion years old.
An extraordinary story
Visitors whose curiosity is whetted by this unusual and varied panorama
are not satisfied with only a few questions and answers. They sense that
here for the asking is an extraordinary _geologic_ (_geo_—earth;
_logic_—science) story. With a little direction, many subtle features
become evident—features that otherwise might escape notice. Here, for
example, is a valley with an odd U-shape. There is a sheer face
crisscrossed with light- and dark-colored rocks. On the valley floor is
a tuft of pine trees that seem to be confined to one particular kind of
rock. On the rolling hills is a layer of peculiar white soil—the only
soil in which coyote dens are common. All these are geologically
controlled phenomena. In short, with a bit of initial guidance, the
viewer gains an ability to observe and to understand so much that the
panorama takes on new depth, vividness, and excitement. It changes from
a flat, two-dimensional picture to a colorful multi-dimensional exhibit
of the earth’s history.
[Illustration: Figure 1. _The Tetons from afar—an astronaut’s view
of the range and adjacent mountains, basins, and plateaus. Width of
area shown in photo is about 100 miles. Stippled pattern marks
boundary of Grand Teton National Park._]
[Illustration: Figure 2. _Sketch of the Teton Range and Jackson
Hole, southwest view. Drawing by J. R. Stacy._
BLOCK DIAGRAM VIEW SOUTHWEST SHOWING THE TETON RANGE AND JACKSON
HOLE]
An astronaut’s view
The Tetons are a short, narrow, and high mountain range, distinctive in
the midst of the great chain of the Rocky Mountains, the backbone of
western North America. Figure 1 shows how the Tetons and their
surroundings might appear if you viewed them from a satellite at an
altitude of perhaps a hundred miles. The U. S. Geological Survey
topographic map of Grand Teton National Park shows the names of many
features not indicated on figure 1 or on the geologic map inside the
back cover. The Teton Range is a rectangular mountain block about 40
miles long and 10-15 miles wide. It is flanked on the east and west by
flat-floored valleys. Jackson Hole is the eastern one and Teton Basin
(called Pierre’s Hole by the early trappers) is the western.
The Teton Range is not symmetrical. The highest peaks lie near the
eastern edge of the mountain block, rather than along its center, as is
true in conventional mountains, and the western slopes are broad and
gentle in contrast to the precipitous eastern slopes. The northern end
of the range disappears under enormous lava flows that form the
Yellowstone Volcanic Plateau. Even from this altitude the outlines of
some of these flows can be seen.
On the south the Teton Range abuts almost at right angles against a
northwest-trending area of lower and less rugged mountains (the Snake
River, Wyoming, and Hoback Ranges). These mountains appear altogether
different from the Tetons. They consist of a series of long parallel
ridges cut or separated by valleys and canyons. This pattern is
characteristic of mountains composed of crumpled, steeply tilted rock
layers—erosion wears away the softer layers, leaving the harder ones
standing as ridges.
On the east and northeast, Jackson Hole is bounded by the Gros Ventre
and Washakie Ranges, which are composed chiefly of folded hard and soft
sedimentary rocks. In contrast, between these mountains and the deepest
part of Jackson Hole to the west, thick layers of soft nearly flat-lying
sedimentary rocks have been sculptured by streams and ice into randomly
oriented knife-edge ridges and rolling hills separated by broad valleys.
The hills east of the park are called the Mount Leidy Highlands and
those northeast are the Pinyon Peak Highlands.
A pilot’s view
If you descend from 100 miles to about 5 miles above the Teton region,
the asymmetry of the range, the extraordinary variety of landscapes, and
the vivid colors of rocks become more pronounced.
Figure 2 shows a panorama of the Teton Range and Jackson Hole from a
vantage point over the Pinyon Peak Highlands. The rough steep slopes and
jagged ridges along the east front of the range contrast with smoother
slopes and more rounded ridges on the western side. Nestled at the foot
of the mountains and extending out onto the floor of Jackson Hole are
tree-rimmed sparkling lakes of many sizes and shapes. Still others lie
in steep-sided rocky amphitheaters near the mountain crests.
One of the most colorful flight routes into Jackson Hole is from the
east, along the north flank of the Gros Ventre Mountains. For 40 miles
this mountain range is bounded by broad parallel stripes of bright-red,
pink, purple, gray, and brown rocks. Some crop out as cliffs or ridges,
and others are _badlands_ (bare unvegetated hills and valleys with steep
slopes and abundant dry stream channels). In places the soft beds have
broken loose and flowed down slopes like giant varicolored masses of
taffy. These are mudflows and landslides. The colorful rocks are bounded
on the south by gray and yellow tilted layers forming snowcapped peaks
of the Gros Ventre Mountains.
These landscapes are the product of many natural forces acting on a
variety of rock types during long or short intervals of geologic time.
Each group of rocks records a chapter in the geologic story of the
region. Other chapters can be read from the tilting, folding, and
breaking of the rocks. The latest episodes are written on the face of
the land itself.
A motorist’s view
Most park visitors first see the Teton peaks from the highway. Whether
they drive in from the south, east, or north, there is one point on the
route at which a spectacular panorama of the Tetons and Jackson Hole
suddenly appears. Part of the thrill of these three views is that they
are so unexpected and so different. The geologic history is responsible
for these differences.
_View north._—
Throughout the first 4 miles north of the town of Jackson, the view of
the Tetons from U. S. 26-89 is blocked by East Gros Ventre Butte. At the
north end of the butte, the highway climbs onto a flat upland at the
south boundary of Grand Teton National Park. Without any advance
warning, the motorist sees the whole east front of the Teton Range
rising steeply from the amazingly flat floor of Jackson Hole.
From the park boundary turnout no lakes or rivers are visible to the
north but the nearest line of trees in the direction of the highest
Teton peaks marks the approximate position of the Gros Ventre River. The
elevation of this river is surprising, for the route has just come up a
150-foot hill, out of the flat valley of a much smaller stream, yet here
at eye-level is a major river perched on an upland plain. The reason for
these strange relations is that the hill is a fault scarp (see fig. 16A
for a diagram) and the valley in which the town of Jackson is located
was dropped 150 feet or more in the last 15,000 years.
On the skyline directly west of the turnout are horizontal and inclined
layers of rocks. These once extended over the tops of the highest peaks
but were worn away from some parts as the mountains rose. All along the
range, trees grow only up to _treeline_ (also called _timberline_—a
general elevation above which trees do not grow) which here is about
10,500 feet above the sea. To the southeast and east, beyond the
sage-covered floor of Jackson Hole, are rolling partly forested slopes
marking the west end of the Gros Ventre Mountains. They do not look at
all like the Tetons because they were formed in a very different manner.
The Gros Ventres are folded mountains that have foothills; the Tetons
are faulted mountains that do not.
Figure 3. _The Teton landscape as seen from Signal Mountain._
[Illustration: A. _View west across Jackson Lake. Major peaks,
canyons, and outcrops of sedimentary rocks are indicated by “s.”_]
[Illustration: B. _View northeast; a study in contrast with the
panorama above._]
Three steepsided hills called _buttes_ rise out of the flat floor of
Jackson Hole. They are tilted and faulted masses of hard, layered rock
that have been shaped by southward-moving glaciers. Six miles north of
the boundary turnout is Blacktail Butte, on the flanks of which are
west-dipping white beds. Southwest of the turnout is East Gros Ventre
Butte, composed largely of layered rocks that are exposed along the road
from Jackson almost to the turnout. These are capped by very young lava
that forms the brown cliff overlooking the highway at the north end of
the butte. To the southwest is West Gros Ventre Butte, composed of
similar rocks.
_View west._—
The motorist traveling west along U. S. 26-287 is treated to two
magnificent views of the Teton Range. The first is 8 miles and the
second 13 miles west of Togwotee Pass. At these vantage points, between
20 and 30 miles from the mountains, the great peaks seem half suspended
between earth and sky—too close, almost, to believe, but too distant to
comprehend.
Only from closer range can the motorist begin to appreciate the size and
steepness of the mountains and to discern the details of their
architecture. The many roads on the floor of Jackson Hole furnish
ever-changing vistas, and signs provided by the National Park Service at
numerous turnouts and scenic overlooks help the visitor to identify
quickly the major peaks and canyons and the principal features of the
valley floor. Of all these roadside vantage points, the top of Signal
Mountain, an isolated hill rising nearly 1,000 feet out of the east
margin of Jackson Lake, probably offers the best overall perspective
(fig. 3). To the west, across the shimmering blue waters of Jackson
Lake, the whole long parade of rugged peaks stretches from the north
horizon to the south, many of the higher ones wearing the tattered
remnants of winter snow. From here, only 8 miles away, the towering
pinnacles, saw-toothed ridges, and deep U-shaped canyons are clearly
visible.
Unlike most other great mountain ranges, the Tetons rise steeply from
the flat valley floor in a straight unbroken line. The high central
peaks tower more than a mile above the valley, but northward and
southward the peaks diminish in height and lose their jagged character,
gradually giving way to lower ridges and rounded hills. Some of the
details of the mountain rock can be seen—gnarled gray rocks of the high
peaks threaded by a fine white lacework of dikes, the dark band that
cleaves through Mount Moran from base to summit, and the light brown and
gray layers on the northern and southern parts of the range.
At first glance the floor of Jackson Hole south of Signal Mountain seems
flat, smooth, and featureless, except for the Snake River that cuts
diagonally across it. Nevertheless, even the flats show a variety of
land forms. The broad sage-covered areas, low isolated hills, and
hummocky tree-studded ridges that form the foreground are all parts of
the Teton landscape, and give us clues to the natural processes that
shaped it. A critical look to the south discloses more strange things.
We take for granted the fact that the sides of normal valleys slope
inward toward a central major stream. South of Signal Mountain, however,
the visitor can see that the Snake River Valley does not fit this
description. The broad flat west of the river should slope east but it
does not. Instead, it has been tilted westward by downward movement
along the Teton fault at the base of the mountains.
_View south._—
About a million motorists drive south from Yellowstone to Grand Teton
National Park each year. As they wind along the crooked highway on the
west brink of Lewis River Canyon (fig. 1), the view south is everywhere
blocked by dense forest. Then, abruptly the road leaves the canyon,
straightens out, and one can look south down a 3-mile sloping avenue cut
through the trees. There, 20 to 30 miles away, framed by the roadway,
are the snow-capped Tetons, with Jackson Lake, luminous in reflected
light, nestled against the east face. This is one of the loveliest and
most unusual views of the mountains that is available to the motorist,
partly because he is 800 feet above the level of Jackson Lake and partly
because this is the only place on a main highway where he can see
clearly the third dimension (width) of the Tetons. The high peaks are on
the east edge; they rise 7,000 feet above the lake but other peaks and
precipitous ridges, progressively diminishing in height, extend on to
the west for a dozen miles (fig. 14). Giant, relatively young lava
flows, into which the Lewis River Canyon was cut, poured southward all
the way to the shore of Jackson Lake and buried the north end of the
Teton Range (figs. 13 and 53). South of Yellowstone Park these flows
were later tilted and broken by the dropping of Jackson Hole and the
rise of the mountains.
A mountaineer’s view
As in many pursuits in life, the greatest rewards of a visit to the
Tetons come to those who expend a real effort to earn them. Only by
leaving the teeming valley and going up into the mountains to hike the
trails and climb the peaks can the visitor come to know the Tetons in
all their moods and changes and view close at hand the details of this
magnificent mountain edifice.
Even a short hike to Hidden Falls and Inspiration Point affords an
opportunity for a more intimate view of the mountains. Along the trail
the hiker can examine outcrops of sugary white granite, glittering
mica-studded dikes, and dark intricately layered rocks. Nearby are great
piles of broken fragments that have fallen from the cliffs above, and
the visitor can begin to appreciate how vulnerable are the towering
crags to the relentless onslaught of frost and snow. The roar of the
foaming stream and the thunder of the falls are constant reminders of
the patient work of running water in wearing away the “everlasting
hills.” Running his hand across one of the smoothly polished rock faces
below Inspiration Point, the hiker gains an unforgettable concept of the
power of glacial ice and its importance in shaping this majestic
landscape. Looking back across Jenny Lake at the encircling ridge of
glacial debris, he can easily comprehend the size of the ancient glacier
that once flowed down Cascade Canyon and emerged onto the floor of
Jackson Hole.
The more ambitious hiker or mountaineer can seek out the inner recesses
of the range and explore other facets of its geology. He can visit the
jewel-like mountain lakes—Solitude, Holly, and Amphitheater are just a
few—cradled in high remote basins left by the Ice Age glaciers. He can
get a closeup view of the Teton Glacier above Amphitheater Lake, or
explore the Schoolroom Glacier, the tiny ice body below Hurricane Pass.
He may follow the trail into Garnet Canyon to see the crystals from
which the canyon takes its name and to examine the soaring ribbonlike
black dike near the end of the trail. In Alaska Basin he can study the
gently tilted layers of sandstone, limestone, and shale that once
blanketed the entire Teton Range and can search for the fossils that
help determine their age and decipher their history. From Hurricane Pass
he can see how these even layers of sedimentary rock have been broken
and displaced and how the older harder rocks that form the highest Teton
peaks have been raised far above them along the Buck Mountain fault.
Of all those who explore the high country, it is the mountaineer who has
perhaps the greatest opportunity to appreciate its geologic story.
Indeed, the success of his climb and his very life may depend on an
intuitive grasp of the mountain geology and the processes that shaped
the peaks. He observes the most intimate details—the inclination of the
joints and fractures, which gullies are swept by falling rocks, which
projecting knobs are firm, and which cracks will safely take a piton. To
many climbers the ascent of a peak is a challenge to technical
competence, endurance, and courage, but to those endowed with curiosity
and a sharp eye it can be much more. As he stands shoulder to shoulder
with the clouds on some windswept peak, such as the Grand Teton, with
the awesome panorama dropping away on all sides, he can hardly avoid
asking how this came to be. What does the mountaineer see that inspires
this curiosity? From the very first glance, it is apparent that the
scenes to the north, south, east, and west are startlingly different.
Looking west from the rough, narrow, weather-ravaged granite summit of
the Grand Teton, one sees far below him the layered gray cliffs of
_marine sedimentary rocks_ (solidified sediment originally deposited in
a shallow arm of the ocean) overlapping the granite and dipping gently
west, finally disappearing under the checkerboard farmland of Teton
Basin. Still farther west are the rolling timbered slopes of the Big
Hole Range in Idaho. A glance at the foreground, 3,000 feet below, shows
some unusual relations of the streams to the mountains. The watershed
divide of the Teton Range is not marked by the highest peaks as one
would expect. Streams in Cascade Canyon and in other canyons to the
north and south begin west of the peaks, bend around them, then flow
eastward in deep narrow gorges cut through the highest part of the
range, and emerge onto the flat floor of Jackson Hole.
In the view north along the crest of the Teton Range, the asymmetry of
the mountains is most apparent. The steep east face culminating in the
highest peaks contrasts with the lower more gentle west flank of the
uplift. From the Grand Teton it is not possible to see the actual place
where the mountains disappear under the lavas of Yellowstone Park, but
the heavily timbered broad gentle surface of the lava plain is visible
beyond the peaks and extends across the entire north panorama. Still
farther north, 75 to 100 miles away, rise the snowcapped peaks (from
northwest to northeast) of the Madison, Gallatin, and Beartooth
Mountains.
The view east presents the greatest contrasts in the shortest
distances—the flat floor of Jackson Hole is 3 miles away and 7,000 feet
below the top of the Grand Teton. Along the junction of the mountains
and valley floor are blue glacial lakes strung out like irregular beads
in a necklace. They are conspicuously rimmed by black-appearing margins
of pine trees that grow only on the surrounding glacial moraines. Beyond
these are the broad treeless boulder-strewn plains of Jackson Hole.
Fifty miles to the east and northeast, on the horizon beyond the rolling
hills of the Pinyon Peak Highlands, are the horizontally layered
volcanic rocks of the Absaroka Range. Southeast is the colorful red,
purple, green, and gray Gros Ventre River Valley, with the fresh giant
scar of the Lower Gros Ventre Slide near its mouth. Bounding the south
side of this valley are the peaks of the Gros Ventre Mountains, whose
tilted slabby gray cliff-forming layers resemble (and are the same as)
those on the west flank of the Teton Range. Seventy miles away, in the
southeast distance, beyond the Gros Ventre Mountains are the shining
snowcapped peaks of the Wind River Range, the highest peak of which
(Gannett Peak) is about 20 feet higher than the Grand Teton.
Conspicuous on the eastern and southeastern skyline are high-level
(11,000-12,000 feet) flat-topped surfaces on both the Wind River and
Absaroka Ranges. These are remnants that mark the upper limit of
sedimentary fill of the basins adjacent to the mountains. A plain once
connected these surfaces and extended westward at least as far as the
conspicuous flat on the mountain south of Lower Gros Ventre Slide. It is
difficult to imagine the amount of rock that has been washed away from
between these remnants in comparatively recent geologic time, during and
after the rise of the Teton Range.
From this vantage point the mountaineer also gets a concept of the
magnitude of the first and largest glaciers that scoured the landscape.
Ice flowed southwestward in an essentially unbroken stream from the
Beartooth Mountains, 100 miles away, westward from the Absaroka Range,
and northwestward from the Wind River Range (fig. 57). Ice lapped up to
treeline on the Teton Range and extended across Jackson Hole nearly to
the top of the Lower Gros Ventre Slide. The Pinyon Peak and Mount Leidy
Highlands were almost buried. All these glaciers came together in
Jackson Hole and flowed south within the ever-narrowing Snake River
Valley.
The view south presents a great variety of contrasts. Conspicuous, as in
the view north, is the asymmetry of the range. South of the high peaks
of crystalline rocks, gray layered cliffs of limestone extend in places
all the way to the steep east face of the Teton Range where they are
abruptly cut off by the great Teton fault.
The flat treeless floor of Jackson Hole narrows southward. Rising out of
the middle are the previously described steepsided ice-scoured rocky
buttes. Beginning near the town of Jackson, part of which is visible,
and extending as far south as the eye can see are row upon row of sharp
ridges and snowcapped peaks that converge at various angles. These are
the Hoback, Wyoming, Salt River, and Snake River Ranges.
CARVING THE RUGGED PEAKS
The rugged grandeur of the Tetons is a product of four geologic factors:
the tough hard rocks in the core, the amount of vertical uplift, the
recency of the mountain-making movement, and the dynamic forces of
destruction. Many other mountains in Wyoming have just as hard rocks in
their cores and an equally great amount of vertical uplift, but they
rose 50 to 60 million years ago and have been worn down by erosion from
that time on. The Tetons, on the other hand, are the youngest range in
Wyoming, less than 10 million years old, and have not had time to be so
deeply eroded.
Steep mountain slopes—the perpetual battleground
Any steep slope or cliff is especially vulnerable to nature’s methods of
destruction. In the Tetons we see the never-ending struggle between two
conflicting factors. The first is the extreme toughness of the rocks and
their consequent resistance to erosion. The second is the presence of
efficient transporting agencies that move out and away from the
mountains all rock debris that might otherwise bury the lower slopes.
The rocks making up most of the Teton Range are among the hardest,
toughest, and least porous known. Therefore, they resist mechanical
disintegration by temperature changes, ice, and water. They consist
predominantly of minerals that are subject to very little chemical decay
in the cold climate of the Tetons.
Absence of weak layers prevents breaking of the tough rock masses under
their own weight. All these conditions, then, are favorable for
preservation of steep walls and high rock pinnacles. Nevertheless, they
do break down. Great piles of broken rock _(talus)_ that festoon the
slopes of all the higher peaks bear witness to the unrelenting assault
by the process of erosion upon the mountain citadels (figs. 4 and 31).
Rock disintegration and gravitational movement
A great variation in both daily and annual temperatures results in
minute amounts of contraction and expansion of rock particles. Repeated
changes in volume produce stress and strain. Although the rocks in the
Tetons are very dense, they eventually yield; a crack forms. Water which
seeps in along this surface of weakness freezes, either overnight or
during long cold spells, and expands, thereby prying a slab of rock away
from the mountain wall. Repeated _frost wedging_, as the process is
called, results eventually in tipping the slab so that it falls.
[Illustration: Figure 4. _Talus at the foot of the jagged
frost-riven peaks around Ice Floe Lake in the south fork of Cascade
Canyon. Photo by Philip Hyde._]
What happens to the rock slab? It may fall and roll several hundred or
thousand feet, depending on the steepness of the mountain surface.
Pieces are broken off as it encounters obstacles. All the fragments find
their way to a valley floor or slope, where they momentarily come to
rest. Thus, rock debris is moved significant and easily observed
distances by gravity.
None of this debris is stationary. If it is mixed with snow or saturated
with water, the whole mass may slowly flow in the same manner as a
glacier. These are called _rock glaciers_; some can be seen on the south
side of Granite Canyon and one, nearly a mile long, is in the valley
north of Eagles Rest Peak.
The countless snow avalanches that thunder down the mountain flanks
after heavy winter snowfalls play their part, too, in gravitational
transport. Loose rocks and debris are incorporated with the moving snow
and borne down the mountainsides to the talus piles below. Trees,
bushes, and soil are swept from the sites of the slides, leaving
conspicuous scars down the slopes and exposing new rock surfaces to the
attack of water and frost. Battered, broken, and uprooted trees along
many of the canyon trails bear silent witness to the awesome power of
snowslides.
These are some of the methods used by Nature in making debris and then,
by means of gravity, clearing it from the mountain slopes. There are
other ways, too. A weak layer of rock (usually one with a lot of clay in
it), parallel to and underlying a mountain slope, may occur between two
hard layers. An extended rainy spell may result in saturation of the
weak zone so that it is well lubricated; then an earthquake or perhaps
merely the weight of the overlying rock sends the now unstable mass
cascading down the slope to the valley below. The famous Lower Gros
Ventre Slide (fig. 5) was formed in this way on June 23, 1925.
Running water cuts and carries
Running water is another effective agent that transports rock debris and
has helped dissect the Teton Range. The damage a broken water main can
wreak on a roadbed is well known, as is the havoc of destructive floods.
The spring floods of streams in the Tetons, swollen by melting snow and
ice (annual precipitation, mostly snow, in the high parts would average
a layer of water 5 feet thick), move some rock debris onto the adjoining
floor of Jackson Hole.
[Illustration: Figure 5. _The Lower Gros Ventre slide, air oblique
view south. The top of the scar is 2,000 feet above the river; the
slide is more than a mile long and one-half mile wide. It dammed the
Gros Ventre River in the foreground, impounding a lake about 200
feet deep and 5 miles long. Gros Ventre Mountains are in the
distance. Photo by P. E. Millward._]
Now and then the range is deluged by summer cloudbursts. Water funnels
down the maze of gullies on the mountainsides, quickly gathering volume
and power, and plunges on to the talus slopes below, as if from gigantic
hoses. The sudden onslaught of these torrents of water on the saturated
unstable talus may trigger enormous rock and mudflows that carry vast
quantities of material down into the canyons. During the summer of 1941
more than 100 of these flows occurred in the park.
Wherever water moves, it carries rock fragments varying in size from
boulders to sand grains and on down to minute clay particles. _Erosion_
(wearing away) by streams is conspicuous wherever the water is muddy, as
it always is each spring in the Snake, Buffalo Fork, and Gros Ventre
Rivers. Clear mountain streams likewise can erode. Although the volume
of material moved and the amount of downcutting of the stream bottom may
not seem great in a single stream, the cumulative effect of many streams
in an area, year after year and century after century, is enormous.
Streams not only transport rocks brought to them by gravitational
movement but also continually widen and deepen their valleys, thereby
increasing the volume of transported debris.
The effectiveness of streams as transporting agents in the Tetons is
enhanced by steep _gradients_ (slopes); these increase water velocity
which in turn expands the capability of the streams to carry larger and
larger rock fragments.
Glaciers scour and transport
Mountain landscapes shaped by frost action, gravitational transport, and
stream erosion alone generally have rounded summits, smooth slopes, and
V-shaped valleys. The jagged ridges, sharply pointed peaks, and deep
U-shaped valleys of the Tetons show that glaciers have played an
important role in their sculpture. The small present-day glaciers still
cradled in shaded recesses among the higher peaks (fig. 6) are but
miniature replicas of great ice streams that occupied the region during
the Ice Age. Evidence both here and in other parts of the world confirms
that glaciers were once far more extensive than they are today.
Glaciers form wherever more snow accumulates during the winter than is
melted during the summer. Gradually the piles of snow solidify to form
ice, which begins to flow under its own weight. Rocks that have fallen
from the surrounding ridges or have been picked up from the underlying
bedrock are incorporated in the moving ice mass and carried along. The
ability of ice to transport huge volumes of rock is easily observed even
in the small present-day glaciers in the Tetons, all of which carry
abundant rock fragments both on and within the ice.
[Illustration: Figure 6. _The Teton Glacier on the north side of
Grand Teton, air oblique view west. Photo by A. S. Post, August 19,
1963._]
Recent measurements show that the ice in the present Teton Glacier (fig.
6) moves nearly 30 feet per year. The ancient glaciers, which were much
wider and deeper, may have moved as much as several hundred feet a year,
like some of the large glaciers in Alaska.
As the glacier moves down a valley, it scours the valley bottom and
walls. The efficiency of ice in this process is greatly increased by the
presence of rock fragments which act as abrasives. The valley bottom is
plowed, quarried, and swept clean of soil and loose rocks. Fragments of
many sizes and shapes are dragged along the bottom of the moving ice and
the hard ones scratch long parallel grooves in the underlying tough
bedrock (fig. 7). Such grooves (_glacial striae_) record the direction
of ice movement.
The effectiveness of glaciers in cutting a U-shaped valley is
particularly striking in Glacier Gulch and Cascade Canyon (figs. 2 and
8).
The rock-walled amphitheater at the head of a glaciated valley is called
a _cirque_ (a good example is at the upper edge of the Teton Glacier,
fig. 6). The steep cirque walls develop by frost action and by quarrying
and abrasive action of the glacier ice where it is near its maximum
thickness. Commonly the glacier scoops out a shallow basin in the floor
of the cirque. Amphitheater Lake, Lake Solitude, Holly Lake, and many of
the other small lakes high in the Teton Range are located in such
basins.
The sharp peaks and the jagged knife-edge ridges so characteristic of
the Tetons are divides left between cirques and valleys carved by the
ancient glaciers.
Effects on Jackson Hole
Rock debris is carried toward the end of the glacier or along the
margins where it is released as the ice melts. The semicircular ridge of
rock fragments that marks the downhill margin of the glacier is called a
_terminal moraine_; that along the sides is a _lateral moraine_ (figs. 9
and 10). These are formed by the slow accumulation of material in the
same manner as that at the end of a conveyor belt. They are not built by
material pushed up ahead of the ice as if by a bulldozer. Large boulders
carried by ice are called _erratics_; many of these are scattered on the
floor of Jackson Hole and on the flanks of the surrounding mountains
(fig. 11).
[Illustration: Figure 7. _Rock surface polished and grooved by ice
on the floor of Glacier Gulch._]
Great volumes of water pour from melting ice near the lower end of a
glacier. These streams, heavily laden with rock flour produced by the
grinding action of the glacier and with debris liberated from the
melting ice, cut channels through the terminal moraine and spread a
broad apron of gravel, sand, and silt down-valley from the glacier
terminus (end). Material deposited by streams issuing from a glacier is
called _outwash_; the sheet of outwash in front of the glacier is called
an _outwash plain_. If the terminus is retreating, masses of old
stagnant ice commonly are buried beneath the outwash; when these melt,
the space they once occupied becomes a deep circular or irregular
depression called a _kettle_ (fig. 12); many of these now contain small
lakes or swamps.
As a glacier retreats, it may build a series of terminal moraines,
marking pauses in the recession of the ice front. Streams issuing from
the ice behind each new terminal moraine are incised more and more
deeply into the older moraines and their outwash plains. Thus, new and
younger layers of bouldery debris are spread at successively lower and
lower levels. These surfaces are called _outwash terraces_.
[Illustration: Figure 8. _East face of the Teton Range showing some
of the glacial features, air oblique view. Cascade Canyon, the
U-shaped valley, was cut by ice. The glacier flowed toward the
flats, occupied the area of Jenny Lake (foreground), and left an
encircling ring of morainal debris, now covered with trees. The flat
bare outwash plain in foreground was deposited by meltwater from the
glacier. The lake occupies a depression that was left when the ice
melted away. National Park Service photo by Bryan Harry._]
[Illustration: Figure 9. _Cutaway view of a typical valley
glacier._]
[Illustration: Figure 10. _Recently-built terminal moraine of the
Schoolroom Glacier, a small ice mass near the head of the south fork
of Cascade Canyon. The present glacier lies to the right just out of
the field of view. The moraine marks a former position of the ice
terminus; the lake (frozen over in this picture) occupies the
depression left when the glacier wasted back from the moraine to its
present position. Crest of the moraine stands about 50 feet above
the lake level. Many of the lakes along the foot of the Teton Range
occupy similar depressions behind older moraines. Photo by Philip
Hyde._]
[Illustration: Figure 11. _Large ice-transported boulder of
coarse-grained pegmatite and granite resting on Cretaceous shale
near Mosquito Creek, on the southwest margin of Jackson Hole. Many
boulders at this locality are composed of pegmatite rock
characteristic of the middle part of the Teton Range. This
occurrence demonstrates that boulders 40 feet in diameter were
carried southward 25 miles and left along the west edge of the ice
stream, 1,500 feet above the base of the glacier on the floor of
Jackson Hole._]
Just as the jagged ridges, U-shaped valleys, and ice-polished rocks of
the Teton Range attest the importance of glaciers in carving the
mountain landscape, the flat gravel outwash plains and hummocky moraines
on the floor of Jackson Hole demonstrate their efficiency in
transporting debris from the mountains and shaping the scenery of the
valley.
Glaciers sculptured all sides of Jackson Hole and filled it with ice to
an elevation between 1,000 and 2,000 feet above the present valley
floor. The visitor who looks eastward from the south entrance to the
park can see clearly glacial scour lines that superficially resemble a
series of terraces on the bare lower slopes of the Gros Ventre
Mountains. Southward-moving ice cut these features in hard rocks.
Elsewhere around the margins of Jackson Hole, especially where the rocks
are soft, evidence that the landscape was shaped by ice has been partly
or completely obliterated by later events. Rising 1,000 feet above the
floor of Jackson Hole are several steepsided buttes (figs. 13 and 55)
described previously, that represent “islands” of hard rock overridden
and abraded by the ice. After the ice melted, these buttes were
surrounded and partly buried by outwash debris.
[Illustration: Figure 12. _“The Potholes,” knob and kettle
topography caused by melting of stagnant ice partly buried by
outwash gravel. Air oblique view north from over Burned Ridge
moraine (see fig. 61 for orientation). Photo by W. B. Hall and J. M.
Hill._]
The story of the glaciers and their place in the geologic history of the
Teton region is discussed in more detail later in this booklet.
[Illustration: Figure 13. _Radar image of part of Tetons and Jackson
Hole. Distance shown between left and right margins is 35 miles.
Lakes from left to right: Phelps, Taggart, Bradley, Jenny, Leigh,
Jackson. Blacktail Butte is at lower left. Channel of Snake River
and outwash terraces are at lower left. Burned Ridge and Jackson
Lake moraines are in center. Lava flows at upper right engulf north
end of Tetons. Striated surfaces at lower right are glacial scour
lines made by ice moving south from Yellowstone National Park. Image
courtesy of National Aeronautics and Space Administration._]
MOUNTAIN UPLIFT
Mountains appear ageless, but as with people, they pass through the
stages of birth, youth, maturity, and old age, and eventually disappear.
The Tetons are youthful and steep and are, therefore, extremely
vulnerable to destructive processes that are constantly sculpturing the
rugged features and carrying away the debris. The mountains are being
destroyed. Although the processes of destruction may seem slow to us, we
know they have been operating for millions of years—so why have the
mountains not been leveled? How did they form in the first place?
Kinds of mountains
There are many kinds of mountains. Some are piles of lava and debris
erupted from a volcano. Others are formed by the bowing up of the
earth’s crust in the shape of a giant dome or elongated arch. Still
others are remnants of accumulated sedimentary rocks that once filled a
basin between preexisting mountains and which are now partially worn
away. An example of this type is the Absaroka Range 40 miles northeast
of the Tetons (figs. 1 and 52).
The Tetons are a still different kind—a _fault block mountain range_
carved from a segment of the earth’s crust that has been uplifted along
a fault. The _Teton fault_ is approximately at the break in slope where
the eastern foot of the range joins the flats at the west edge of
Jackson Hole (see map inside back cover), but in most places is
concealed beneath glacial deposits and debris shed from the adjacent
steep slopes. The shape of the range and its relation to Jackson Hole
have already been described. Clues as to the presence of the fault are:
(1) the straight and deep east face of the Teton Range, (2) absence of
foothills, (3) asymmetry of the range (fig. 14), and (4) small _fault
scarps_ (cliffs or steep slopes formed by faulting) along the mountain
front (fig. 15).
[Illustration: Figure 14. _Air oblique view south showing the width
and asymmetry of Teton Range. Grand Teton is left of center and Mt.
Moran is the broad humpy peak still farther left. Photo taken
October 1, 1965_.]
Recent geophysical surveys of Jackson Hole combined with data from deep
wells drilled in search of oil and gas east of the park also yield
valuable clues. By measuring variations in the earth’s magnetic field
and in the pull of gravity and by studying the speed of shock waves
generated by small dynamite explosions, Dr. John C. Behrendt of the U.
S. Geological Survey has determined the depth and tilt of rock layers
buried beneath the veneer of glacial debris and stream-laid sand and
gravel on the valley floor. This information was used in constructing
the geologic cross section in the back of the booklet. The same rock
layers that cap the summit of Mount Moran (fig. 27) are buried at depths
of nearly 24,000 feet beneath the nearby floor of Jackson Hole but are
cut off by the Teton fault at the west edge of the valley. Thus the
approximate amount of movement along the fault here would be about
30,000 feet.
Anatomy of faults
The preceding discussion shows that the Tetons are an upfaulted mountain
block. Why is this significant? The extreme youth of the Teton fault,
its large amount of displacement, and the fact that the newly upfaulted
angular mountain block was subjected to intense glaciation are among the
prime factors responsible for the development of the magnificent alpine
scenery of the Teton Range. An understanding of the anatomy of faults
is, therefore, pertinent.
[Illustration: Figure 15. _Recent fault scarp (arrows indicate base)
offsetting alluvial fan at foot of Rockchuck Peak. View west from
Cathedral Group scenic turnout. National Park Service photo by W. E.
Dilley and R. A. Mebane._]
A fault is a plane or zone in the earth’s crust along which the rocks on
one side have moved in relation to the rocks on the other. There are
various kinds of faults just as there are various types of mountains.
Three principal types of faults are present in the Teton region: normal
faults, reverse faults, and thrust faults. A _normal fault_ (fig. 16A)
is a steeply _dipping_ (steeply inclined) fault along which rocks above
the fault have moved _down_ relative to those beneath it. A _reverse
fault_ (fig. 16B) is a steeply inclined fault along which the rocks
above the fault have moved _up_ relative to those below it. A _thrust
fault_ (fig. 16C) is a gently inclined fault along which the principal
movement has been more nearly horizontal than vertical.
Normal faults may be the result of tension or pulling apart of the
earth’s crust or they may be caused by adjustment of the rigid crust to
the flow of semi-fluid material below. The crust sags or collapses in
areas from which the subcrustal material has flowed and is bowed up and
stretched in areas where excess subcrustal material has accumulated. In
both areas the adjustments may result in normal faults.
Reverse faults are generally caused by compression of a rigid block of
the crust, but some may also be due to lateral flow of subcrustal
material.
Thrust faults are commonly associated with tightly bent or folded rocks.
Many of them are apparently caused by severe compression of part of the
crust, but some are thought to have formed at the base of slides of
large rock masses that moved from high areas into adjacent low areas
under the influence of gravity.
The Teton fault (see cross section inside back cover) is a normal fault;
the Buck Mountain fault, which lies west of the main peaks of the Teton
Range, is a reverse fault. No thrust faults have been recognized in the
Teton Range, but the mountains south and southwest of the Tetons (fig.
1) display several enormous thrust faults along which masses of rocks
many miles in extent have moved tens of miles eastward and
northeastward.
Time and rate of uplift
When did the Tetons rise?
A study of the youngest sedimentary rocks on the floor of Jackson Hole
shows that the Teton Range began to rise rapidly and take its present
shape less than 9 million years ago. The towering peaks themselves are
direct evidence that the rate of uplift far exceeded the rate at which
the rising block was worn away by erosion. The mountains are still
rising, and comparatively rapidly, as is indicated by small faults
cutting the youngest deposits (fig. 15).
How rapidly? Can the rate be measured?
We know that in less than 9 million years (and probably in less than 7
million years) there has been 25,000 to 30,000 feet of displacement on
the Teton fault. This is an average of about 1 foot in 300-400 years.
The movement probably was not continuous but came as a series of jerks
accompanied by violent earthquakes. One fault on the floor of Jackson
Hole near the southern boundary of the park moved 150 feet in the last
15,000 years, an average of 1 foot per 100 years.
In view of this evidence of recent crustal unrest, it is not surprising
that small earthquakes are frequent in the Teton region. More violent
ones can probably be expected from time to time.
Figure 16. _Types of faults._
[Illustration: A.—Normal fault (tensional)]
[Illustration: B.—Reverse fault (compressional)]
[Illustration: C.—Thrust fault (compressional)]
Why are mountains here?
Why did the Tetons form where they are?
At the beginning of this booklet we discussed briefly the two most
common theories of origin of mountains: continental drift and convection
currents. The question of why mountains are where they are and more
specifically why the Tetons are here remains a continuing scientific
challenge regardless of the wealth of data already accumulated in our
storehouse of knowledge.
The mobility of the earth’s crust is an established fact. Despite its
apparent rigidity, laboratory experiments demonstrate that rocks flow
when subjected to extremely high pressures and temperatures. If the
stress exceeds the strength at a given pressure and temperature, the
rock breaks. Flowing and fracturing are two of the ways by which rocks
adjust to the changing environments at various levels in the earth’s
crust. These acquired characteristics, some of which can be duplicated
in the laboratory, are guides by which we interpret the geologic history
of rocks that once were deep within the earth.
The site of the Teton block no doubt reflects hidden inequalities at
depth. We cannot see these, nor in this area can we drill below the
outer layer of the earth; nevertheless, measurements of gravity and of
the earth’s magnetic field clearly show that they exist.
We know that the Tetons rose at the time Jackson Hole collapsed but the
volume of the uplifted block is considerably less than that of the
downdropped block. This, then, was not just a simple case in which all
the subcrustal material displaced by the sinking block was squeezed
under the rising block (the way a hydraulic jack works). What happened
to the rest of the material that once was under Jackson Hole? It could
not be compressed so it had to go somewhere.
As you look northward from the top of the Grand Teton or Mount Moran, or
from the main highway at the north edge of Grand Teton National Park,
you see the great smooth sweep of the volcanic plateau in Yellowstone
National Park. Farther off to the northeast are the strikingly layered
volcanic rocks of the Absaroka Range (fig. 52). For these two areas, an
estimate of the volume of volcanic rock that reached the surface and
flowed out, or was blown out and spread far and wide by wind and water,
is considerably in excess of 10,000 cubic miles. On the other hand, this
volume is many times more than that displaced by the sagging and
downfaulting of Jackson Hole.
Where did the rest of the volcanic material come from? Is it pertinent
to our story? Teton Basin, on the west side of the Teton Range, and the
broad Snake River downwarp farther to the northwest (fig. 1) are
sufficiently large to have furnished the remainder of the volcanic
debris. As it was blown out of vents in the Yellowstone-Absaroka area,
its place could have been taken deep underground by material that moved
laterally from below all three downdropped areas. The movement may have
been caused by slow convection currents within the earth, or perhaps by
some other, as yet unknown, force. The sagging of the earth’s crust on
both sides of the Teton Range as well as the long-continued volcanism
are certainly directly related to the geologic history of the park.
In summary, we theorize as to how the Tetons rose and Jackson Hole sank
but are not sure why the range is located at this particular place, why
it trends north, why it rose so high, or why this one, of all the
mountain ranges surrounding the Yellowstone-Absaroka volcanic area, had
such a unique history of uplift. These are problems to challenge the
minds of generations of earth scientists yet to come.
The restless land
Among the greatest of the park’s many attractions is the solitude one
can savor in the midst of magnificent scenery. Only a short walk
separates us from the highway, torrents of cars, noise, and tension.
Away from these, everything seems restful.
Quiescent it may seem, yet the landscape is not static but dynamic. This
is one of the many exciting ideas that geology has contributed to
society. The concept of the “everlasting hills” is a myth. All the
features around us are actually rather short-lived in terms of geologic
time. The discerning eye detects again and again the restlessness of the
land. We have discussed many bits of evidence that show how the
landscape and the earth’s crust beneath it are constantly being carved,
pushed up, dropped down, folded, tilted, and faulted.
The Teton landscape is a battleground, the scene of a continuing
unresolved struggle between the forces that deform the earth’s crust and
raise the mountains and the slow processes of erosion that strive to
level the uplands, fill the hollows, and reduce the landscape to an
ultimate featureless plain. The remainder of this booklet is devoted to
tracing the seesaw conflict between these inexorable antagonists through
more than 2.5 billion years as they shaped the present landscape—and the
battle still goes on.
Evidence of the struggle is all around us. Even though to some observers
it may detract from the restfulness of the scene, perhaps it conveys to
all of us a new appreciation of the tremendous dynamic forces
responsible for the magnificence of the Teton Range.
The battle is indicated by the small faults that displace both the land
surface and young deposits at the east base of Mount Teewinot, Rockchuck
Peak (fig. 15), and other places along the foot of the Tetons.
Jackson Hole continues to drop and tilt. The gravel-covered surfaces
that originally sloped southward are now tilted westward toward the
mountains. The Snake River, although the major stream, is not in the
lowest part of Jackson Hole; Fish Creek, a lesser tributary near the
town of Wilson, is 15 feet lower. For 10 miles this creek flows
southward parallel to the Snake River but with a gentler gradient, thus
permitting the two streams to join near the south end of Jackson Hole.
As tilting continues, the Snake River west of Jackson tries to move
westward but is prevented from doing so by long flood-control levees
built south of the park.
Recent faults also break the valley floor between the Gros Ventre River
and the town of Jackson.
The ever-changing piles of rock debris that mantle the slopes adjacent
to the higher peaks, the creeping advance of rock glaciers, the
devastating snow avalanches, and the thundering rockfalls are specific
reminders that the land surface is restless. Jackson Hole contains more
landslides and rock mudflows than almost any other part of the Rocky
Mountain region. They constantly plague road builders (fig. 17) and add
to the cost of other types of construction.
All of these examples of the relentless battle between constructive and
destructive processes modifying the Teton landscape are but minor
skirmishes. The bending and breaking of rocks at the surface are small
reflections of enormous stresses and strains deep within the earth where
the major conflict is being waged. It is revealed every now and then by
a convulsion such as the 1959 earthquake in and west of Yellowstone
Park. Events of this type release much more energy than all the nuclear
devices thus far exploded by man.
[Illustration: Figure 17. _Slide blocking main highway in northern
part of Grand Teton National Park. National Park Service photo by
Eliot Davis, May 1952._]
ENORMOUS TIME AND DYNAMIC EARTH
Framework of time
One of geology’s greatest philosophical contributions has been the
demonstration of the enormity of geologic time. Astronomers deal with
distances so great that they are almost beyond understanding; nuclear
physicists study objects so small that we can hardly imagine them.
Similarly, the geologist is concerned with spans of time so immense that
they are scarcely comprehensible. Geology is a science of time as well
as rocks, and in our geologic story of the Teton region we must refer
frequently to the geologic time scale, the yardstick by which we measure
the vast reaches of time in earth history.
Rocks and relative age
Very early in the science of geology it was recognized that in many
places one can tell the comparative ages of rocks by their relations to
one another. For example, most _sedimentary rocks_ are consolidated
accumulations of large or small rock fragments and were deposited as
nearly horizontal layers of gravel, sand, or mud. In an undisturbed
sequence of sedimentary rocks, the layer on the bottom was deposited
first and the layer on top was deposited last. All of these must, of
course, be younger than any previously formed rock fragments
incorporated in them.
_Igneous rocks_ are those formed by solidification of molten material,
either as lava flows on the earth’s surface (_extrusive igneous rocks_)
or at depth within the earth (_intrusive igneous rocks_). The relative
ages of extrusive igneous rocks can often be determined in much the same
way as those of sedimentary strata. A lava flow is younger than the
rocks on which it rests, but older than those that rest on top of it.
An intrusive igneous rock must be younger than the rocks that enclosed
it at the time it solidified. It may contain pieces of the enclosing
rocks that broke off the walls and fell into the liquid. Pebbles of the
igneous rock that are incorporated in nearby sedimentary layers indicate
that the sediments must be somewhat younger.
All of these criteria tell us only that one rock is older or younger
than another. They tell us little about the absolute age of the rocks or
about how much older one is than the other.
Fossils and geologic time
Fossils provide important clues to the ages of the rocks in which they
are found. The slow evolution of living things through geologic time can
be traced by a systematic study of fossils. The fossils are then used to
determine the relative ages of the rocks that contain them and to
establish a geologic time scale that can be applied to fossil-bearing
rocks throughout the world. Figure 18 shows the major subdivisions of
the last 600 million years of geologic time and some forms of life that
dominated the scene during each of these intervals. Strata containing
closely related fossils are grouped into _systems_; the time interval
during which the strata comprising a particular system were deposited is
termed a _period_. The periods are subdivisions of larger time units
called _eras_ and some are split into smaller time units called
_epochs_. Strata deposited during an epoch comprise a _series_. Series
are in turn subdivided into rock units called _groups_ and formations.
Expressed in tabular form these divisions are:
Subdivisions of Time-rock units Rock units
geologic time
Era
Period System
Epoch Series
Group
Formation
The time scale based on the study of fossil-bearing sedimentary rocks is
called the stratigraphic time scale; it is given in table 1. The
subdivisions are arranged in the same order in which they were
deposited, with the oldest at the bottom and the youngest at the top.
All rocks older than Cambrian (the first period in the Paleozoic Era)
are classed as Precambrian. These rocks are so old that fossils are rare
and therefore cannot be conveniently used as a basis for subdivision.
The stratigraphic time scale is extremely useful, but it has serious
drawbacks. It can be applied only to fossil-bearing strata or to rocks
whose ages are determined by their relation to those containing fossils.
It cannot be used directly for rocks that lack fossils, such as igneous
rocks, or metamorphic rocks in which fossils have been destroyed by heat
or pressure. It is used to establish the relative ages of sedimentary
strata throughout the world, but it gives no information as to how long
ago a particular layer was deposited or how many years a given period or
era lasted.
Radioactive clocks
The measurement of geologic time in terms of years was not possible
until the discovery of natural radioactivity. It was found that certain
atoms of a few elements spontaneously throw off particles from their
nuclei and break down to form atoms of other elements. These decay
processes take place at constant rates, unaffected by heat, pressure, or
chemical conditions. If we know the rate at which a particular
radioactive element decays, the length of time that has passed since a
mineral crystal containing the elements formed can be calculated by
comparing the amount of the radioactive element remaining in the crystal
with the amount of disintegration products present.
[Illustration: Figure 18. _Major subdivisions of the last 600
million years of geologic time and some of the dominant forms of
life._]
MILLIONS OF
YEARS AGO
0 Man
0-60 CENOZOIC QUATERNARY and TERTIARY Mammals
60-130 MESOZOIC CRETACEOUS
130-180 JURASSIC Dinosaurs
180-220 TRIASSIC
220-260 PALEOZOIC PERMIAN Reptiles
260-350 PENNSYLVANIAN, Amphibians
MISSISSIPPIAN
350-400 DEVONIAN Fishes
400-440 SILURIAN Sea scorpions
440-500 ORDOVICIAN Nautiloids
500-530 CAMBRIAN Trilobites
530- PRECAMBRIAN Soft-bodied
creatures
Three principal radioactive clocks now in use are based on the decay of
uranium to lead, rubidium to strontium, and potassium to argon. They are
effective in dating minerals millions or billions of years old. Another
clock, based on the decay of one type of carbon (_Carbon-14_) to
nitrogen, dates organic material, but only if it is less than about
40,000 years old.
The uranium, rubidium, and potassium clocks are especially useful in
dating igneous rocks. By determining the absolute ages of igneous rocks
whose stratigraphic relations to fossil-bearing strata are known, it is
possible to estimate the number of years represented by the various
subdivisions of the stratigraphic time scale.
The yardstick of geologic time
Recent estimates suggest that the earth was formed at least 4.5 billion
years ago. To visualize the length of geologic time and the relations
between the stratigraphic and absolute time scales, let us imagine a
yardstick as representing the length of time from the origin of the
earth to the present (fig. 19). On one side of the yardstick we plot
time in years; on the other, we plot the divisions of the stratigraphic
time scale according to the most reliable absolute age determinations.
[Illustration: Table 1. The stratigraphic time scale.]
Era System or period Series or epoch
Cenozoic Quaternary Recent
Pleistocene
Tertiary Pliocene
Miocene
Oligocene
Eocene
Paleocene
Mesozoic Cretaceous
Jurassic
Triassic
Paleozoic Permian
Pennsylvanian
Mississippian
Devonian
Silurian[1]
Ordovician
Cambrian
— Precambrian
[1]_The Silurian is the only major subdivision of the stratigraphic time
scale not represented in Grand Teton National Park._
We are immediately struck by the fact that all of the subdivisions of
the stratigraphic time scale since the beginning of the Paleozoic are
compressed into the last 5 inches of our yardstick! All of the other 31
inches represent Precambrian time. We also see that subdivisions of the
stratigraphic time scale do not represent equal numbers of years. We use
smaller and smaller subdivisions as we approach the present. (Notice the
subdivisions of the Tertiary and Quaternary in table 1 that are too
small to show even in the enlarged part of figure 19). This is because
the record of earth history is more vague and incomplete the farther
back in time we go. In effect, we are very nearsighted in our view of
time. This “geological myopia” becomes increasingly evident throughout
the remainder of this booklet.
[Illustration: Figure 19. _The geologic time scale—our yardstick in
time._]
ABSOLUTE TIME (Years ago) INCHES STRATIGRAPHIC TIME SCALE
First man → 0 CENOZOIC
1 MESOZOIC
First dinosaurs → 2 PALEOZOIC
3
500 million 4
First abundant fossils → 5 PRECAMBRIAN
6
7
1 billion 8
9
10
11
12
13
14
Oldest known fossils → 15
2 billion 16
17
18
19
20
21
22
23
3 billion 24
25
26
27
Oldest dated rocks → 28
29
30
31
4 billion 32
33
34
35
Minimum age of the earth → 36
ENLARGEMENT OF THE LAST SIX INCHES
ABSOLUTE TIME INCHES STRATIGRAPHIC TIME SCALE
(Years Ago)
0 0 CENOZOIC QUATERNARY
TERTIARY
MESOZOIC CRETACEOUS
1 JURASSIC
TRIASSIC
2 PALEOZOIC PERMIAN
PENNSYLVANIAN
MISSISSIPPIAN
3 DEVONIAN
SILURIAN
ORDOVICIAN
500 million 4 CAMBRIAN
5 PRECAMBRIAN
6
PRECAMBRIAN ROCKS—THE CORE OF THE TETONS
The visitor who looks at the high, rugged peaks of the Teton Range is
seeing rocks that record about seven-eighths of all geologic time. These
Precambrian rocks are part of the very foundation of the continent and
are therefore commonly referred to by geologists as basement rocks. In
attempting to decipher their origin and history we peer backward through
the dim mists of time, piecing together scattered clues to events that
occurred billions of years ago, perhaps during the very birth of the
North American Continent. To cite an oft-quoted example, it is as though
we were attempting to read the history of an ancient and long-forgotten
civilization from the scattered unnumbered pages of a torn manuscript,
written in a language that we only partially understand.
Ancient gneisses and schists
The oldest Precambrian rocks in the Teton Range are layered gneisses and
schists exposed over wide areas in the northern and southern parts of
the range and as scattered isolated masses in the younger granite that
forms the high peaks in the central parts. The layered gneisses may be
seen easily along the trails in the lower parts of Indian Paintbrush and
Death Canyons, and near Static Peak.
The _layered gneisses_ are composed principally of quartz, feldspar,
_biotite_ (black mica), and _hornblende_ (a very dark-green or black
mineral commonly forming rodlike crystals). Distinct layers, a few
inches to several feet thick, contain different proportions of these
minerals and account for the banded appearance. Layers composed almost
entirely of quartz and feldspar are light-gray or white, whereas darker
gray layers contain higher proportions of biotite and hornblende.
Some layers are dark-green to black _amphibolite_, composed principally
of hornblende but with a little feldspar and quartz. In many places the
gneisses include layers of _schist_, a flaky rock, much of which is
mica. At several places on the east slopes of Mount Moran thin layers of
impure gray marble are found interleaved with the gneisses. West of
Static Peak along the Alaska Basin Trail a heavy dark rock with large
amounts of _magnetite_ (strongly magnetic black iron oxide) occurs as
layers in the gneiss.
In some places the gneiss contains dark-reddish crystals of garnet as
much as an inch in diameter. Commonly the garnet crystals are surrounded
by white “halos” which lack biotite or hornblende, probably because the
constituents necessary to form these minerals were absorbed by the
garnet crystals. In Death Canyon and on the slopes of Static Peak some
layers of gray gneiss contain egg-shaped masses of magnetite as much as
one-half inch in diameter (fig. 20). These masses are likewise
surrounded by elliptical white halos and have the startling appearance
of small eyes peering from the rock. Appropriately, this rock has been
called the “bright-eyed” gneiss by Prof. Charles C. Bradley in his
published study (Wyoming Geological Association, 1956) of this area.
What were the ancient rocks from which the gneisses of the Teton Range
were formed? Most of the evidence has been obliterated but a few
remaining clues enable us to draw some general conclusions. The banded
appearance of many of the gneisses suggests that they were formed from
sedimentary and volcanic rocks that accumulated on the sea floor near a
chain of volcanic islands—perhaps somewhat similar to the modern
Aleutians or the islands of Indonesia. When these deposits were buried
deep in the earth’s crust the chemical composition of some layers may
have undergone radical changes. Other layers, however, still have
compositions resembling those of younger rocks elsewhere whose origins
are better known. For example, the layers of impure marble were probably
once beds of sandy limestone, and the lighter colored gneiss may have
been muddy sandstone, possibly containing volcanic ash. Some dark
amphibolite layers could represent altered lava flows or beds of
volcanic ash; others may have resulted from the addition of silica to
muddy magnesium-rich limestone during metamorphism. The magnetite-rich
gneiss probably was originally a sedimentary iron ore.
[Illustration: Figure 20. _“Bright-eyed” gneiss from Death Canyon.
The dark magnetite spots are about ¼ inch in diameter. The
surrounding gneiss is composed of quartz, feldspar, and biotite, but
biotite is missing in the white halos around the magnetite._]
Minerals that were most easily altered at depth reacted with one another
to form new minerals more “at home” under the high temperature and
pressure in this environment just as the ingredients in a cake react
when heated in an oven. Rocks formed by such processes are called
_metamorphic rocks_; careful studies of the minerals that they contain
suggest that the layered gneisses developed at temperatures as high as
1000°F at depths of 5 to 10 miles. Under these conditions the rocks must
have behaved somewhat like soft taffy as is shown by layers that have
been folded nearly double without being broken (fig. 21). Folds such as
these range from fractions of an inch to thousands of feet across and
are found in gneisses throughout the Teton Range. In a few places folds
are superimposed in such a way as to indicate that the rocks were
involved in several episodes of deformation in response to different
sets of stress during metamorphism.
When did these gneisses form? Age determinations of minerals containing
radioactive elements show that granite which was intruded into them
after they were metamorphosed and folded is more than 2.5 billion years
old. They must, therefore, be older than that. Thus, they probably are
at least a billion years older than rocks containing the first faint
traces of life on earth and 2 billion years older than the oldest rocks
containing abundant fossils. How much older is not known, but the
gneisses are certainly among the oldest rocks in North America and
record some of the earliest events in the building of this continent.
Figure 21. _Folds in layered gneisses._
[Illustration: A. _North face of the ridge west of Eagles Rest Peak.
The face is about 700 feet high. Notice the extreme contortion of
the gneiss layers._]
[Illustration: B. _Closeup view of some of the folds near the bottom
of the face in figure A. The light-colored layers are composed
principally of quartz and feldspar. The darker layers are rich in
hornblende._]
Irregular bodies of granite gneiss are interleaved with the layered
gneisses in the northern part of the Teton Range. The _granite gneiss_
is relatively coarse grained, streaky gray or pink, and composed
principally of quartz, feldspar, biotite, and hornblende. It differs
from enclosing layered gneisses in its coarser texture, lack of
layering, and more uniform appearance. The dark minerals (biotite and
hornblende) are concentrated in thin discontinuous wisps that give the
rock its streaky appearance.
The largest body of granite gneiss is exposed in a belt 1 to 2 miles
wide and 10 miles long extending northeastward from near the head of
Moran Canyon, across the upper part of Moose Basin, and into the lower
reaches of Webb Canyon. This gneiss may have been formed from granite
that invaded the ancient sedimentary and volcanic rocks before they were
metamorphosed, or it may have been formed during metamorphism from some
of the sediments and volcanics themselves.
At several places in Snowshoe, Waterfalls, and Colter Canyons the
layered gneisses contain discontinuous masses a few tens or hundreds of
feet in diameter of heavy dark-green or black _serpentine_. This rock is
frequently called “_soapstone_” because the surface feels smooth and
soapy to the touch. Indians carved bowls (fig. 22) from similar material
obtained from the west side of the Tetons and from the Gros Ventre
Mountains to the southeast. Pebbles of serpentine along streams draining
the west side of the Tetons have been cut and polished for jewelry and
sold as “_Teton jade_”; it is much softer and less lustrous than real
jade. The serpentine was formed by metamorphism of dark-colored igneous
rocks lacking quartz and feldspar.
Granite and pegmatite
Contrary to popular belief, _granite_ (crystalline igneous rock composed
principally of quartz and feldspar) forms only a part of the Teton
Range. The Grand Teton (fig. 6) and most surrounding subsidiary peaks
are sculptured from an irregular mass of granite exposed continuously
along the backbone of the range from Buck Mountain northward toward
upper Leigh Canyon. The rock is commonly fine grained, white or
light-gray, and is largely composed of crystals of gray quartz and white
feldspar about the size and texture of the grains in very coarse lump
sugar. Flakes of black or dark-brown mica (biotite) and silvery white
mica (_muscovite_) about the size of grains of pepper are scattered
through the rock.
From the floor of Jackson Hole the granite cliffs and buttresses of the
high peaks appear nearly white in contrast to the more somber grays and
browns of surrounding gneisses and schists. These dark rocks are laced
by a network of irregular light-colored granite dikes ranging in
thickness from fractions of an inch to tens of feet (fig. 23).
[Illustration: Figure 22. _Indian bowls carved from soapstone,
probably from the Teton Range. Mouth of the unbroken bowl is about 4
inches in diameter._]
The largest masses of granite contain abundant unoriented angular blocks
and slabs of the older gneisses. These inclusions range from a few
inches in diameter (fig. 24) to slabs hundreds of feet thick and
thousands of feet long.
Dikes or irregular intrusions of pegmatite are found in almost every
exposure of granite. _Pegmatite_ contains the same minerals as granite
but the individual mineral crystals are several inches or even as much
as a foot in diameter.
Some pegmatites contain silvery plates or tabular crystals of muscovite
mica as much as 6 inches across that can be split into transparent
sheets with a pocket knife. Others have dark-brown biotite mica in
crystals about the size and shape of the blade of a table knife.
A few pegmatites contain scattered red-brown crystals of garnet ranging
in size from that of a BB shot to a small marble; a few in Garnet Canyon
and Glacier Gulch are larger than baseballs (fig. 25). The garnets are
fractured and many are partly altered to _chlorite_ (a dull-green
micaceous mineral) so they are of no value as gems.
Figure 23. _Dikes of granite and pegmatite._
[Illustration: A. _Network of light-colored granite dikes on the
northeast face of the West Horn on Mt. Moran. The dikes cut through
gneiss in which the layers slant steeply downward to the left. The
face is about 700 feet high. Snowfield in the foreground is at the
edge of the Falling Ice Glacier._]
[Illustration: B. _Irregular dike of granite and pegmatite cutting
through dark layered gneisses near Wilderness Falls in Waterfalls
Canyon. The cliff face is about 80 feet high. Contacts of the dike
are sharp and angular and cut across the layers in the enclosing
gneiss._]
Pegmatite _dikes_ (tabular bodies of rock that, while still molten, were
forced along fractures in older rocks) commonly cut across granite
dikes, but in many places the reverse is true. Some dikes are composed
of layers of pegmatite alternating with layers of granite (fig. 26),
showing that the pegmatite and granite are nearly contemporaneous. Prof.
Bruno Giletti and his coworkers at Brown University, using the
rubidium-strontium radioactive clock, determined that the granite and
pegmatite in the Teton Range are about 2.5 billion years old.
[Illustration: Figure 24. _Angular blocks of old streaky granite
gneiss in fine-grained granite northwest of Lake Solitude. The
difference in orientation of the streaks in the gneiss blocks
indicates that the blocks have been rotated with respect to one
another and that the fine-grained granite must therefore have been
liquid at the time of intrusion. A small light-colored dike in the
upper left-hand block of gneiss ends at the edge of the block; it
intruded the gneiss before the block was broken off and incorporated
in the granite. A small dike of pegmatite cuts diagonally through
the granite just to the left of the hammer and extends into the
blocks of gneiss at both ends. This dike was intruded after the
granite had solidified. Thus, in this one small exposure we can
recognize four ages of rocks: the streaky granite gneiss, the
light-colored dike, the fine-grained granite, and the small
pegmatite dike._]
Black dikes
Even the most casual visitor to the Teton Range notices the remarkable
black band that extends down the east face of Mount Moran (figs. 27 and
28) from the summit and disappears into the trees north of Leigh Lake.
This is the outcropping edge of a steeply inclined dike composed of
_diabase_, a nearly black igneous rock very similar to basalt. Thinner
diabase dikes are visible on the east face of Middle Teton, on the south
side of the Grand Teton, and in several other places in the range (see
geologic map inside back cover).
[Illustration: Figure 25. _Garnet crystal in pegmatite. The crystal
is about 6 inches in diameter. Other minerals are feldspar (white)
and clusters of white mica flakes. The mica crystals appear dark in
the photograph because they are wet._]
The diabase is a heavy dark-greenish-gray to black rock that turns rust
brown on faces that have been exposed to the weather. It is studded with
small lath-shaped crystals of feldspar that are greenish gray in the
fresh rock and milk white on weathered surfaces.
The black dikes formed from molten rock that welled up into nearly
vertical fissures in the older Precambrian rocks. Toward the edges of
the dikes the feldspar laths in the diabase become smaller and smaller
(fig. 29), indicating that the wall rocks were relatively cool when the
_magma_ or melted rock was intruded. Rapid chilling at the edges
prevented growth of large crystals. In many places hot solutions from
the dike permeated the wall rocks, staining them rosy red.
[Illustration: Figure 26. _A small dike of pegmatite and granite
cutting through folded layered gneiss in Death Canyon.
Coarse-grained pegmatite forms most of the dike, but fine-grained
granite is found near the center. Small offshoots of the dike
penetrate into the wall rocks. The dike cuts straight across folds
in the enclosing gneisses and must therefore have been intruded
after development of the folds. The white ruler is about 6 inches
long._]
The black dike on Mount Moran is about 150 feet thick near the summit of
the peak. This dike has been traced westward for more than 7 miles.
Where it passes out of the park south of Green Lakes Mountain it is 100
feet thick. The amount of molten material needed to form the exposed
segment of this single dike could fill Jenny Lake three times over. The
other dikes are thinner and not as long: the dike on Middle Teton is 20
to 40 feet thick, and the dike on Grand Teton is 40 to 60 feet thick.
[Illustration: Figure 27. _Air oblique view of the east face of Mt.
Moran, showing the great black dike. Main mass of the mountain is
layered gneiss and streaky granite gneiss. White lines are dikes of
granite and pegmatite; light-gray mound on the summit is about 50
feet of Cambrian sedimentary rock (Flathead Sandstone). Notice that
the black dike cuts across the dikes of granite and pegmatite but
that its upper edge is covered by the much younger layer of
sandstone. Falling Ice Glacier is in the left center; Skillet
Glacier is in the lower right center. Photo by A. S. Post.
University of Washington, August 19, 1963._]
[Illustration: Figure 28. _The great black dike on the east face of
Mt. Moran. The dike is about 150 feet thick and its vertical extent
in the picture is about 3,000 feet. The fractures in the dike
perpendicular to its walls are cracks formed as the liquified rock
cooled and crystallized. Falling Ice Glacier is in the center.
National Park Service photo by H. D. Pownall._]
[Illustration: Figure 29. _Closeup view of the edge of the Middle
Teton black dike exposed on the north wall of Garnet Canyon near the
west end of the trail. Dike rock (diabase) is on the right; wall
rock (gneiss) is on the left. Match shows scale._]
The black dikes must be the youngest of the Precambrian units because
they cut across all other Precambrian rocks. The dikes must have been
intruded before the beginning of Cambrian deposition inasmuch as they do
not cut the oldest Cambrian beds. Gneiss adjacent to the dike on Mount
Moran contains biotite that was heated and altered about 1.3 billion
years ago according to Professor Giletti. The alteration is believed to
have occurred when the dike was emplaced; therefore this and similar
dikes elsewhere in the range are probably about 1.3 billion years old.
Quartzite
At about the same time as the dikes were being intruded in the Tetons,
many thousands of feet of sedimentary rocks, chiefly sandstone, were
deposited in western Montana, 200 miles northwest of Grand Teton
National Park. The sandstone was later recrystallized and recemented and
became a very dense hard rock called _quartzite_. Similar quartzite,
possibly part of the same deposit, was laid down west of the north end
of the Teton Range, within the area now called the Snake River downwarp
(fig. 1).
The visitor who hikes or camps anywhere on the floor of Jackson Hole
becomes painfully aware of the thousands upon thousands of remarkably
rounded hard quartzite boulders. He wonders where they came from because
nowhere in the adjacent mountains is this rock type exposed. The answer
is that the quartzites were derived from a long-vanished uplift (figs.
42 and 46), carried eastward by powerful rivers past the north end of
the Teton Range, and then were deposited in a vast sheet of gravel that
covered much of Jackson Hole 60 to 80 million years ago. Since then,
these virtually indestructible boulders have been re-worked many times
by streams and ice, yet still retain the characteristics of the original
ancient sediments.
A backward glance
So far we have seen that the Precambrian basement exposed in the Teton
Range contains a complex array of rocks of diverse origins and various
ages. Before passing on to the younger rocks, reference to our yardstick
may help to place the Precambrian events in their proper perspective.
In all of Precambrian time, which encompasses more than 85 percent of
the history of the earth (31 of the 36 inches of our yardstick), only
two events are dated in the Teton Range: the intrusion of granite and
pegmatite about 2.5 billion years ago, and the emplacement of the black
dikes about 1.3 billion years ago. These dates are indicated by heavy
arrows on the time scale (fig. 30). The ancient gneisses and schists
were formed sometime before 2.5 billion years ago, and probably are no
older than 3.5 billion years, the age of the oldest rocks dated anywhere
in the world.
The close of the Precambrian—end of the beginning
More than 700 million years elapsed between intrusion of the black dikes
and deposition of the first Paleozic sedimentary rocks—a longer period
of time than has elapsed since the beginning of the Paleozic Era. During
this enormous interval the Precambrian rocks were uplifted, exposed to
erosion, and gradually worn to a nearly featureless plain, perhaps
somewhat resembling the vast flat areas in which similar Precambrian
rocks are now exposed in central and eastern Canada. At the close of
Precambrian time, about 600 million years ago, the plain slowly
floundered and the site of the future Teton Range disappeared beneath
shallow seas that were to wash across it intermittently for the next 500
million years. It is to the sediments deposited in these seas that we
turn to read the next chapter in the geologic story of the Teton Range.
[Illustration: Figure 30. _A glance at the yardstick. The geologic
time scale shows positions of principal events recorded in the
Precambrian rocks of the Tetons._]
ABSOLUTE TIME (Years ago) INCHES
Beginning of the Paleozoic. First abundant fossils → 4
1 billion 8
Maximum age of black dikes → 10
Oldest known fossils 15
2 billion 16
Old granite and pegmatite 20
3 billion 24
Gneisses and schists formed sometime in this interval 20-27
Oldest dated rocks → 28
4 billion → 32
Minimum age of the earth 36
THE PALEOZOIC ERA—TIME OF LONG-VANISHED SEAS AND THE DEVELOPMENT OF LIFE
The Paleozoic sequence
North, west, and south of the highest Teton peaks the soaring spires and
knife-edge ridges of Precambrian rock give way to rounded spurs and
lower flat-topped summits, whose slopes are palisaded by continuous gray
cliffs that resemble the battlements of some ancient and long-abandoned
fortress (fig. 31). As mentioned previously, the cliffs are the
projecting edges of layers of sedimentary rocks of Paleozoic age that
accumulated in or along the margins of shallow seas. At one time the
layers formed a thick unbroken, nearly horizontal blanket across the
Precambrian basement rocks, but subsequent uplift of the eastern edge of
the Teton fault block tilted them westward. They were then stripped from
the highest peaks.
The Paleozoic and younger sedimentary rocks in the Teton region are
subdivided into _formations_, each of which is named. A formation is
composed of rock layers which, because of their similar physical
characteristics, can be distinguished from overlying and underlying
layers. They must be thick enough to be shown on a geologic map. Table 2
lists the various Paleozoic formations present in and adjacent to Grand
Teton National Park and gives their thicknesses and characteristics.
These sedimentary rocks are of special interest, for they not only
record an important chapter of geologic history but elsewhere in the
region they contain petroleum and other mineral deposits.
The Paleozoic rocks can be viewed close at hand from the top of the
Teton Village tram (fig. 32) on the south boundary of the park. A less
accessible but equally spectacular exposure of Paleozoic rocks is in
Alaska Basin, along the west margin of the park, where they are stacked
like even layers in a gigantic cake (fig. 33).
Alaska Basin—site of an outstanding rock and fossil record
Strata in Alaska Basin record with unusual clarity the opening chapters
in the chronicle of seas that flowed and ebbed across the future site of
the Teton Range during most of the Paleozoic Era. In the various rock
layers are inscribed stories of the slow advance and retreat of ancient
shorelines, of the storm waves breaking on long-vanished beaches, and of
the slow and intricate evolution of the myriads of sea creatures that
inhabited these restless waters.
[Illustration: Figure 31. _Paleozoic rocks on the west flank of the
Teton Range, air oblique view west. Ragged peaks in the foreground
(Buck Mountain on the left center, Mt. Wister, with top outlined by
snow patch on the extreme right), are carved in Precambrian rocks.
Banded cliffs in the background are sedimentary rocks. Alaska Basin
is at upper right. Teton Basin, a broad, extensively farmed valley
in eastern Idaho, is at top. Photo by A. S. Post, University of
Washington, 1963._]
Careful study of the fossils allows us to determine the age of each
formation (table 3). Even more revealing, the fossils themselves are
tangible evidence of the orderly parade of life that crossed the Teton
landscape during more than 250 million years. Here is a record of
Nature’s experiments with life, the triumphs, failures, the bizarre, the
beautiful.
[Illustration: Table 2.—Paleozoic sedimentary rocks exposed in the
Teton region.]
Age Formation Thickness Description Where exposed
(feet)
Permian Phosphoria 150-250 Dolomite, gray, North and west
Formation cherty, sandy, flanks of Teton
black shale and Range, north
phosphate beds; flank of Gros
marine. Ventre Mountains,
southern Jackson
Hole.
Pennsylvanian Tensleep 600-1,500 Tensleep Sandstone, North and west
and Amsden light-gray, hard, flanks of Teton
Formations underlain by Range, north
Amsden Formation, flank of Gros
a domolite and red Ventre Mountains,
shale with a basal southern Jackson
red sandstone; Hole.
marine.
Mississippian Madison 1,000-1,200 Limestone, North and west
Limestone blue-gray, hard, flanks of Teton
fossiliferous; Range, north
thin red shale in flank of Gros
places near top; Ventre Mountains,
marine. southern Jackson
Hole.
Devonian Darby 200-500 Dolomite, dark-gray North and west
Formation to brown, fetid, flanks of Teton
hard, and brown, Range, north
black, and yellow flank of Gros
shale; marine. Ventre Mountains,
southern Jackson
Hole.
Ordovician Bighorn 300-500 Dolomite, North and west
Dolomite light-gray, flanks of Teton
siliceous, very Range, north and
hard; white dense west flanks of
very fine-grained Gros Ventre
dolomite at top; Mountains,
marine. southern Jackson
Hole.
Cambrian Gallatin 180-300 Limestone, blue North and west
Limestone gray, hard, flanks of Teton
thin-bedded; Range and Gros
marine. Ventre Mountains.
Gros Ventre 600-800 Shale, green, North and west
Formation flaky, with Death flanks of Teton
Canyon Limestone Range and Gros
Member composed of Ventre Mountains.
about 300 feet of
hard cliff-forming
limestone in
middle; marine.
Flathead 175-200 Sandstone, North and west
Sandstone reddish-brown, flanks of Teton
very hard, Range and Gros
brittle; partly Ventre Mountains.
marine.
The regularity and parallel relations of the layers in well-exposed
sections such as the one in Alaska Basin suggest that all these rocks
were deposited in a single uninterrupted sequence. However, the fossils
and regional distribution of the rock units show that this is not really
the case. The incomplete nature of this record becomes apparent if we
plot the ages of the various formations on the absolute geologic time
scale (fig. 34). The length of time from the beginning of the Cambrian
Period to the end of the Mississippian Period is about 285 million
years. The strata in Alaska Basin are a record of approximately 120
million years. More than half of the pages in the geologic story are
missing even though, compared with most other areas, the book as a whole
is remarkably complete! During these unrecorded intervals of time either
no sediments were deposited in the area of the Teton Range or, if
deposited, they were removed by erosion.
[Illustration: Figure 32. _Paleozoic marine sedimentary rocks near
south boundary of Grand Teton National Park. View is south from top
of Teton Village tram. National Park Service photo by W. E. Dilley
and R. A. Mebane._]
Madison Limestone
Darby Formation
Bighorn Dolomite
Gallatin Limestone
Advance and retreat of Cambrian seas: an example
The first invasion and retreat of the Paleozoic sea are sketched on
figure 35. Early in Cambrian time a shallow seaway, called the
_Cordilleran trough_, extended from southern California northeastward
across Nevada into Utah and Idaho (fig. 35A). The vast gently rolling
plain on Precambrian rocks to the east was drained by sluggish
westward-flowing rivers that carried sand and mud into the sea. Slow
subsidence of the land caused the sea to spread gradually eastward. Sand
accumulated along the beaches just as it does today. As the sea moved
still farther east, mud was deposited on the now-submerged beach sand.
In the Teton area, the oldest sand deposit is called the Flathead
Sandstone (fig. 36).
The mud laid down on top of the Flathead Sandstone as the shoreline
advanced eastward across the Teton area is now called the Wolsey Shale
Member of the Gros Ventre Formation. Some shale shows patterns of cracks
that formed when the accumulating mud was briefly exposed to the air
along tidal flats. Small phosphatic-shelled animals called _brachiopods_
inhabited these lonely tidal flats (fig. 37A and 37B) but as far as is
known, nothing lived on land. Many shale beds are marked with faint
trails and borings of wormlike creatures, and a few contain the remains
of tiny very intricately developed creatures with head, eyes, segmented
body, and tail. These are known as trilobites (fig. 37C and 37D).
Descendants of these lived in various seas that crossed the site of the
dormant Teton Range for the next 250 million years.
[Illustration: Figure 33. _View southwest across Alaska Basin,
showing tilted layers of Paleozoic sedimentary rocks on the west
flank of the Teton Range. National Park Service photo._]
Mount Meek
Madison Limestone
Bighorn Dolomite
Death Canyon Limestone Member
Flathead Sandstone
Precambrian Rock
As the shoreline moved eastward, the Death Canyon Limestone Member of
the Gros Ventre Formation (fig. 33) was deposited in clear water farther
from shore. Following this the sea retreated to the west for a short
time. In the shallow muddy water resulting from this retreat the Park
Shale Member of the Gros Ventre Formation was deposited. In places
underwater “meadows” of algae flourished on the sea bottom and built
extensive reefs (fig. 38A). From time to time shoal areas were hit by
violent storm waves that tore loose platy fragments of recently
solidified limestone and swept them into nearby channels where they were
buried and cemented into thin beds of jumbled fragments (fig. 38B)
called _“edgewise” conglomerate_. These are widespread in the shale and
in overlying and underlying limestones.
[Illustration: Table 3. _Formations exposed in Alaska Basin._]
AGE (Numbers FORMATION (Thickness) ROCKS AND FOSSILS
show age in
millions of
years)
(310)
MISSISSIPPIAN MADISON LIMESTONE Uniform thin beds of
(Total about 1,100 blue-gray limestone and
feet, but only lower sparse very thin layers of
300 feet preserved in shale. Brachiopods, corals,
this section) and other fossils abundant.
(345)
LATE AND DARBY FORMATION (About Thin beds of gray and buff
MIDDLE DEVONIAN 350 feet) dolomite interbedded with
layers of gray, yellow, and
black shale. A few fossil
brachiopods, corals, and
bryozoans.
(390)
(425)
LATE AND BIGHORN DOLOMITE (About Thick to very thin beds of
MIDDLE 450 feet; Leigh blue-gray or brown dolomite,
ORDOVICIAN Dolomite Member about white on weathered surfaces.
40 feet thick at top) A few broken fossil
brachiopods, bryozoans, and
horn corals. Thin beds of
white fine-grained dolomite
at top are the Leigh Member.
(440)
(500)
LATE CAMBRIAN GALLATIN LIMESTONE (180 Blue-gray limestone mottled
feet) with irregular rusty or
yellow patches. Trilobites
and brachiopods.
(530)
MIDDLE CAMBRIAN GROS VENTRE FORMATION
PARK SHALE MEMBER Gray-green shale containing
(220 feet) beds of platy limestone
conglomerate. Trilobites,
brachiopods, and fossil algal
heads.
DEATH CANYON Two thick beds of
LIMESTONE MEMBER dark-blue-gray limestone
(285 feet) separated by 15 to 20 feet of
shale that locally contains
abundant fossil brachiopods
and trilobites.
WOLSEY SHALE MEMBER Soft greenish-gray shale
(100 feet) containing beds of purple and
green sandstone near base. A
few fossil brachiopods.
FLATHEAD LIMESTONE (175 Brown, maroon, and white
feet) sandstone, locally containing
many rounded pebbles of
quartz and feldspar. Some
beds of green shale at top.
(570)
PRECAMBRIAN Granite, gneiss, and
pegmatite.
[Illustration: Figure 34. _Absolute ages of the formations in Alaska
Basin. Shaded parts of the scale show intervals for which there is
no record._]
STRATIGRAPHIC SCALE ABSOLUTE ENLARGED PIECE OF
TIME (Years YARDSTICK SHOWN ON
ago) FIGURE 19
2
PALEZOIC PENNSYLVANIAN ?
300 million
MISSISSIPPIAN MADISON
DEVONIAN DARBY
3
400 million
SILURIAN
ORDOVICIAN BIGHORN
500 million 4
CAMBRIAN GALLATIN
GROS VENTRE
FLATHEAD
600 million
PRECAMBRIAN 5
Figure 35. _The first invasions of the Paleozoic sea._
[Illustration: A. _In Early Cambrian time an arm of the Pacific
Ocean occupied a deep trough in Idaho, Nevada, and part of Utah. The
land to the east was a broad gently rolling plain of Precambrian
rocks drained by sluggish westward-flowing streams. The site of the
Teton Range was part of this plain. Slow subsidence of the land
caused the sea to move eastward during Middle Cambrian time flooding
the Precambrian plain._]
[Illustration: B. _By Late Cambrian time the sea had drowned all of
Montana and most of Wyoming. The Flathead Sandstone and Gros Ventre
Formation were deposited as the sea advanced. The Gallatin Limestone
was being deposited when the shoreline was in about the position
shown in this drawing._]
[Illustration: C. _In Early Ordovician time uplift of the land
caused the sea to retreat back into the trough, exposing the
Cambrian deposits to erosion. Cambrian deposits were partly stripped
off of some areas. The Bighorn Dolomite was deposited during the
next advance of the sea in Middle and Late Ordovician time._]
[Illustration: Figure 36. _Conglomeratic basal bed of Flathead
Sandstone and underlying Precambrian granite gneiss; contact is
indicated by a dark horizontal line about 1 foot below hammer. This
contact is all that is left to mark a 2-billion year gap in the rock
record of earth history. The locality is on the crest of the Teton
Range 1 mile northwest of Lake Solitude._]
Once again the shoreline crept eastward, the seas cleared, and the
Gallatin Limestone was deposited. The Gallatin, like the Death Canyon
Limestone Member, was laid down for the most part in quiet, clear water,
probably at depths of 100 to 200 feet. However, a few beds of “edgewise”
conglomerate indicate the occurrence of sporadic storms. At this time,
the sea covered all of Idaho and Montana and most of Wyoming (fig. 35B)
and extended eastward across the Dakotas to connect with shallow seas
that covered the eastern United States. Soon after this maximum stage
was reached slow uplift caused the sea to retreat gradually westward.
The site of the Teton Range emerged above the waves, where, as far as is
now known, it may have been exposed to erosion for nearly 70 million
years (fig. 35C).
The above historical summary of geologic events in Cambrian time is
recorded in the Cambrian formations. This is an example of the
reconstructions, based on the sedimentary rock record, that have been
made of the Paleozoic systems in this area.
Figure 37. _Cambrian fossils in Grand Teton National Park._
A-B. _Phosphatic-shelled brachiopods, the oldest fossils found in
the park. Actual width of specimens is about ¼ inch._
C-D. _Trilobites. Width of C is ¼ inch, D is ½ inch. National Park
Service photos by W. E. Dilley and R. A. Mebane._
[Illustration: A.]
[Illustration: B.]
[Illustration: C.]
[Illustration: D.]
Younger Paleozoic formations
Formations of the remaining Paleozoic systems are likewise of interest
because of the ways in which they differ from those already described.
Figure 38. _Distinctive features of Cambrian rocks._
[Illustration: A. _Algal heads in the Park Shale Member of the Gros
Ventre Formation. These calcareous mounds were built by algae
growing in a shallow sea in Cambrian time. They are now exposed on
the divide between North and South Leigh Creeks, nearly 2 miles
above sea level!_]
[Illustration: B. _Bed of “edgewise” conglomerate in the Gallatin
Limestone. Angular plates of solidified lime-ooze were torn from the
sea bottom by storm waves, swept into depressions, and then buried
in lime mud. These fragments, seen in cross section, make the
strange design on the rock. Thin limestone beds below are
undisturbed. National Park Service photo by W. E. Dilley._]
The Bighorn Dolomite of Ordovician age forms ragged hard massive
light-gray to white cliffs 100 to 200 feet high (figs. 32 and 33).
_Dolomite_ is a calcium-magnesium carbonate, but the original sediment
probably was a calcium carbonate mud that was altered by magnesium-rich
sea water shortly after deposition. Corals and other marine animals were
abundant in the clear warm seas at this time.
Dolomite in the Darby Formation of Devonian age differs greatly from the
Bighorn Dolomite; that in the Darby is dark-brown to almost black, has
an oily smell, and contains layers of black, pink, and yellow mudstone
and thin sandstone. The sea bottom during deposition of these rocks was
foul and frequently the water was turbid. Abundant fossil fragments
indicate fishes were common for the first time. Exposures of the Darby
Formation are recognizable by their distinctive dull-yellow thin-layered
slopes between the prominent gray massive cliffs of formations below and
above.
The Madison Limestone of Mississippian age is 1,000 feet thick and is
exposed in spectacular vertical cliffs along canyons in the north, west,
and south parts of the Tetons. It is noted for the abundant remains of
beautifully preserved marine organisms (fig. 39). The fossils and the
relatively pure blue-gray limestone in which they are embedded indicate
deposition in warm tranquil seas. The beautiful Ice Cave on the west
side of the Tetons and all other major caves in the region were
dissolved out of this rock by underground water.
The Pennsylvanian System is represented by the Amsden Formation and the
Tensleep Sandstone. Cliffs of the Tensleep Sandstone can be seen along
the Gros Ventre River at the east edge of the park. The Amsden, below
the Tensleep, consists of red and green shale, sandstone, and thin
limestone. The shale is especially weak and slippery when exposed to
weathering and saturated with water. These are the strata that make up
the glide plane of the Lower Gros Ventre Slide (fig. 5) east of the
park.
The Phosphoria Formation and its equivalents of Permian age are unlike
any other Paleozoic rocks because of their extraordinary content of
uncommon elements. The formation consists of sandy dolomite, widespread
black phosphate beds and black shale that is unusually rich not only in
phosphorus, but also in vanadium, uranium, chromium, zinc, selenium,
molybdenum, cobalt, and silver. The formation is mined extensively in
nearby parts of Idaho and in Wyoming for phosphatic fertilizer, for the
chemical element phosphorus, and for some of the metals that can be
derived from the rocks as byproducts. These elements and compounds are
not everywhere concentrated enough to be of economic interest, but their
dollar value is, in a regional sense, comparable to that of some of the
world’s greatest mineral deposits.
Figure 39. _A glimpse of the sea floor during deposition of the
Madison Limestone 330 million years ago, showing the remains of
brachiopods, corals, and other forms of life that inhabited the
shallow warm water._
[Illustration: A. _Slab in which fossils are somewhat broken and
scattered. Scale slightly reduced. National Park Service photo by W.
E. Dilley and R. A. Mebane._]
[Illustration: B. _Slab in which fossils are remarkably complete.
Silver dollar gives scale. Specimen is in University of Wyoming
Geological Museum._]
THE MESOZOIC—ERA OF TRANSITION
The Mesozoic Era in the Teton region was a time of alternating marine,
transitional, and continental environments. Moreover, the highly
diversified forms of life, ranging from marine mollusks to tremendous,
land-living dinosaurs, confirm and reinforce the story of the rocks.
Living things, too, were in transition, for as environment changed, many
forms moved from the sea to land in order to survive. It was the time
when some of the most spectacularly colored rock strata of the region
were deposited.
Colorful first Mesozoic strata
Bright-red soft Triassic rocks more than 1,000 feet thick, known as the
Chugwater Formation, comprise most of the basal part of the Mesozoic
sequence (table 4). They form colorful hills east and south of the park.
The red color is caused by a minor amount of iron oxide. Mud cracks and
the presence of fossil reptiles and amphibians indicate deposition in a
tidal flat environment, with the sea lying several miles southwest of
Jackson Hole. A few beds of white _gypsum_ (calcium sulfate) are
present; they were apparently deposited during evaporation of shallow
bodies of salt water cut off from the open sea.
As the Triassic Period gave way to the Jurassic, salmon-red windblown
sand (Nugget Sandstone) spread across the older red beds and in turn was
buried by thin red shale and thick gypsum deposits of the Gypsum Spring
Formation. Then down from Alaska and spreading across most of Wyoming
came the _Sundance Sea_, a warm, muddy, shallow body of water that
teemed with marine mollusks. In it more than 500 feet of highly
fossiliferous soft gray shale and thin limestones and sandstones were
deposited. The sea withdrew and the Morrison and Cloverly Formations
(Jurassic and Lower Cretaceous) were deposited on low-lying tropical
humid flood plains. These rocks are colorful, consisting of red, pink,
purple, and green badland-forming claystones and mudstones, and yellow
to buff sandstones. Vegetation was abundant and large and small
dinosaurs roamed the countryside or inhabited the swamps.
[Illustration: Table 4.—Mesozoic sedimentary rocks exposed in the
Teton region.]
Age Formation Thickness Description Where exposed
(feet)
CRETACEOUS
Harebell 0-5,000 Sandstone, olive Eastern and
Formation drab, silty, drab northeastern parts
siltstone, and of Jackson Hole.
dark-gray shale;
thick beds of
quartzite pebble
conglomerate in
upper part.
Meeteetse 0-700 Sandstone, gray to Spread Creek area.
Formation chalky white,
blue-green to gray
siltstone, thin
coal, and green to
yellow bentonite.
Mesaverde 0-1,000 Sandstone, white, Eastern Jackson
Formation massive, soft, thin Hole.
gray shale, sparse
coal.
Unnamed 3,500± Sandstone and Eastern Jackson
sequence of shale, gray to Hole and eastern
lenticular brown; abundant margin of the park.
sandstone, coal in lower 2,000
shale, and feet.
coal.
Bacon Ridge 900-1,200 Sandstone, light Eastern Jackson
Sandstone gray, massive, Hole and eastern
marine, gray shale, margin of the park.
many coal beds.
Cody Shale 1,300-2,200 Shale, gray, soft; Eastern and
thin green northern parts of
sandstone, some Jackson Hole.
bentonite; marine.
Frontier 1,000 Sandstone, gray, Eastern and
Formation and black to gray northern parts and
shale, marine; many south-western
persistent white margin of Jackson
bentonite beds in Hole.
lower part.
Mowry Shale 700 Shale, Gros Ventre River
silvery-gray, hard, Valley, northern
siliceous, with margin of the park,
many fish scales; and southern part
thin bentonite of Jackson Hole.
beds; marine.
Thermopolis 150-200 Shale, black, soft, Gros Ventre River
Shale fissile, with Valley, northern
persistent margin of the park,
sandstone at top; and southern part
marine. of Jackson Hole.
Cloverly and 650 Sandstone, light North end of Teton
Morrison(?) gray, sparkly, Range and Gros
Formations rusty near top, Ventre River Valley.
underlain by
variegated soft
claystone; basal
part is silty
dully-variegated
sandstone and
claystone.
JURASSIC
Sundance 500-700 Sandstone, green, North end of Teton
Formation underlain by soft Range, Blacktail
gray shale and thin Butte, Gros Ventre
highly River Valley.
fossiliferous
limestones; marine.
Gypsum Spring 75-100 Gypsum, white, North end of Teton
Formation interbedded with Range, Blacktail
red shale and gray Butte, Gros Ventre
dolomite; partly River Valley.
marine.
Nugget 0-350 Sandstone, North flank of Gros
Sandstone salmon-red, hard. Ventre Mountains,
southern Jackson
Hole.
TRIASSIC
Chugwater 1,000-1,500 Siltstone and North flank of Gros
Formation shale, red, Ventre Mountains,
thin-bedded; one north end of Teton
thin marine Range, southernmost
limestone in upper Jackson Hole.
third.
Dinwoody 200-400 Siltstone, brown, North flank of Gros
Formation hard, thin-bedded; Ventre Mountains,
marine. north end of Teton
Range, southernmost
Jackson Hole.
Drab Cretaceous strata
The youngest division of the _Mesozoic_ Era is the Cretaceous Period.
Near the beginning of this period, brightly colored rocks continued to
be deposited. Then, the Teton region, as well as most of Wyoming, was
partly, and at times completely, submerged by shallow muddy seas. As a
result, the brightly variegated strata were covered by 10,000 feet of
generally drab-colored sand, silt, and clay containing some coal beds,
volcanic ash layers, and minor amounts of gravel.
The Cretaceous sea finally retreated eastward from the Teton region
about 85 million years ago, following the deposition of the Bacon Ridge
Sandstone (fig. 40). As it withdrew, extensive coal swamps developed
along the sea coast. The record of these swamps is preserved in coal
beds 5 to 10 feet thick in the Upper Cretaceous deposits. The coal beds
are now visible in abandoned mines along the east margin of the park.
Coal is formed from compacted plant debris; about 5 feet of this
material is needed to form 1 inch of coal. Thus, lush vegetation must
have flourished for long periods of time, probably in a hot wet climate
similar to that now prevailing in the Florida Everglades.
Sporadically throughout Cretaceous time fine-grained ash was blown out
of volcanoes to the west and northwest and deposited in quiet shallow
water. Subsequently the ash was altered to a type of clay called
_bentonite_ that is used in the foundry industry and in oil well
drilling muds. In Jackson Hole, the elk and deer lick bentonite
exposures to get a bitter salt and, where the beds are water-saturated,
enjoy “stomping” on them. Bentonite swells when wet and causes many
landslides along access roads into Jackson Hole (fig. 17).
The Cretaceous rocks in the Teton region are part of an enormous
east-thinning wedge that here is nearly 2 miles thick. Most of the
debris was derived from slowly rising mountains to the west.
Cretaceous sedimentary rocks are much more than of just scientific
interest; they contain mineral deposits important to the economy of
Wyoming and of the nation. Wyoming leads the States in production of
bentonite, all of it from Cretaceous rocks. These strata have yielded
far more oil and gas than any other geologic system in the State and the
production is geographically widespread. They also contain enormous coal
reserves, some in beds between 50 and 100 feet thick. The energy
resources alone of the Cretaceous System in Wyoming make it invaluable
to our industrialized society.
[Illustration: Figure 40. _The yardstick and the sea. The shaded
part of the yardstick shows the 500-million-year interval during
which Paleozoic and Mesozoic seas swept intermittently across the
future site of the Tetons. When they finally withdrew about 85
million years ago, a little more than 5/8 of an inch of the
yardstick remained to be accounted for._]
ABSOLUTE TIME (Millions of years ago) INCHES
{submerged} 85-585 ⅝-4⅝
CENOZOIC 0-80 0-½
MESOZOIC 80-180 ½-⅞
PALEOZOIC 180-570 ⅞-4⅞
PRECAMBRIAN 570- 4⅞-
As the end of the Cretaceous Period approached, slightly more than 80
million years ago, the flat monotonous landscape (fig. 41) which had
prevailed during most of Late Cretaceous time gave little hint that the
stage was set for one of the most exciting and important chapters in the
geologic history of North America.
Birth of the Rocky Mountains
The episode of mountain building that resulted in formation of the
ancestral Rocky Mountains has long been known as the _Laramide
Revolution_. West and southwest of Wyoming, mountains had already
formed, the older ones as far away as Nevada and as far back in time as
Jurassic, the younger ones rising progressively farther east, like giant
waves moving toward a coast. The first crustal movement in the Teton
area began in latest Cretaceous time when a broad low northwest-trending
arch developed in the approximate area of the present Teton Range and
Gros Ventre Mountains. However, this uplift bore no resemblance to the
Tetons as we know them today for the present range formed 70 million
years later.
[Illustration: Figure 41. _Grand Teton National Park region slightly
more than 80 million years ago, just before onset of Laramide
Revolution. The last Cretaceous sea still lingered in central
Wyoming._]
One bit of evidence (there are others) of the first Laramide mountain
building west of the Tetons is a tremendous deposit of quartzite boulder
debris (several hundred cubic miles in volume) derived from the _Targhee
uplift_ (fig. 42). Nowhere is the uplift now exposed, but from the size,
composition, and distribution of rock fragments that came from it, we
know that it was north and west of the northern end of the present-day
Teton Range. Powerful streams carried boulders, sand, and clay eastward
and southeastward across the future site of Jackson Hole and deposited
them in the Harebell Formation (table 4). Mingled with this sediment
were tiny flakes of gold and a small amount of mercury. Fine-grained
debris was carried still farther east and southeast into two enormous
depositional troughs in central and southern Wyoming. Most of the large
rock fragments were derived from Precambrian and possibly lower
Paleozoic quartzites. This means that at least 15,000 feet of overlying
Paleozoic and Mesozoic strata must first have been stripped away from
the Targhee uplift before the quartzites were exposed to erosion.
[Illustration: Figure 42. _Teton region at the end of Cretaceous
time about 65 million years ago. The ancestral Teton-Gros Ventre
uplift had risen and prominent southeastward drainage from the
Targhee uplift was well established. See figure 41 for State lines
and location map._]
Remains of four-legged horned ceratopsian dinosaurs, possibly
_Triceratops_ (fig. 43), reflecting the last population explosion of
these reptiles, have been found in pebbly sandstone of the Harebell
Formation in highway cuts on the Togwotee Pass road 8 miles east of the
park.
[Illustration: Figure 43. _Triceratops, a horned dinosaur of the
type that inhabited Jackson Hole about 65 million years ago. Sketch
by S. H. Knight._]
Near the end of Cretaceous time, broad gentle uplifts also began to stir
at the sites of future mountain ranges in many parts of Wyoming. The
ancestral Teton-Gros Ventre arch continued to grow. Associated with and
parallel to it was a series of sharp steepsided elongated
northwest-trending upfolds (_anticlines_). One of these can be seen
where it crosses the highway at the Lava Creek Campground near the
eastern margin of Grand Teton National Park.
During these episodes of mountain building, erosion, and deposition, the
dinosaurs became extinct all over the world. The “Age of Mammals” was
about to begin.
TERTIARY—TIME OF MAMMALS, MOUNTAINS, LAKES, AND VOLCANOES
[Illustration: Figure 44. _The last inch of the yardstick, enlarged
to show subdivisions of the Cenozoic Era._]
STRATIGRAPHIC SCALE THE LAST INCH OF ABSOLUTE TIME (million
THE YARDSTICK years ago)
CENOZOIC
QUATERNARY
Recent and 0 0
Pleistocene
TERTIARY
Pliocene 0 0
Miocene ⅛ 12
Oligocene ¼ 25
Eocene ⅜ 40
Paleocene ⁷/₁₆ 55
MESOZOIC
CRETACEOUS ½ 65
The Cenozoic (table 1), last and shortest of the geologic eras,
comprises the Tertiary and Quaternary Periods. It began about 65 million
years ago and is represented by only the final one-half inch of our
imaginary yardstick of time (fig. 19). Nevertheless, it is the era
during which the Tetons rose in their present form and the landscape was
sculptured into the panorama of beauty that we now see. In order to show
the many Tertiary and Quaternary events in the Teton region, it is
necessary to enlarge greatly the last part of the yardstick (fig. 44).
There are two reasons for the extraordinarily clear and complete record.
First, the Teton region was a relatively active part of the earth’s
crust, characterized by many downdropped blocks. The number of events is
great and their records are preserved in sediments trapped in the
subsiding basins. Second, the geologically recent past is much easier to
see than the far dimmer, distant past; the rocks that record later
events are fresher, less altered, more complete, and more easily
interpreted than are those that tell us of older events.
[Illustration: Table 5.—Cenozoic sedimentary rocks and
unconsolidated deposits in the Teton region.]
Age Formation Thickness Description Where exposed
(feet)
QUATERNARY
Recent
Modern 0-200± Sand, gravel, and Floor of Jackson
stream, silt along present Hole and in canyons
landslide, streams; jumbled and on
glacial and broken rock in mountainsides
talus deposits landslides and on throughout the
talus slopes; region.
debris around
existing glaciers.
Pleistocene
Glacial 0-200± Gravel, sand, silt, Floor of Jackson
deposits and and glacial debris. Hole.
loess
Unnamed upper 0-500 Shale, brown-gray, Gros Ventre River
lake sequence sandstone, and Valley.
conglomerate.
Unnamed lower 0-200 Shale, siltstone, National Elk Refuge.
lake sequence and sandstone,
gray, green, and
red.
? Pleistocene or Pliocene
Bivouac 0-1,000 Conglomerate, with Signal Mountain and
Formation purplish-gray West Gros Ventre
welded tuff in Butte.
upper part.
TERTIARY
Pliocene
Teewinot 0-6,000 Limestone, tuff, National Elk
Formation and claystone, Refuge, Blacktail
white, soft. Butte, and eastern
margin of Antelope
Flat.
Camp Davis 0-5,500 Conglomerate, red Southernmost tip of
Formation and gray, with Jackson Hole.
white tuff,
diatomite, and red
and white claystone.
Miocene
Colter 0-7,000 Volcanic Pilgrim and Ditch
Formation conglomerate, tuff, Creeks, and north
and sandstone, end of Teton Range.
white to
green-brown, with
locally-derived
basalt and andesite
rock fragments.
Oligocene
Wiggins 0-3,000 Volcanic Eastern margin of
Formation conglomerate, gray Jackson Hole.
to brown, with
white tuff layers.
Eocene
Unnamed upper 0-1,000 Tuff, conglomerate, Eastern margin of
and middle sandstone, and Jackson Hole.
Eocene claystone, green,
sequence underlain by
variegated
claystone and
quartzite pebble
conglomerate.
Wind River 2,000-3,000 Claystone and Eastern margin of
and Indian sandstone, Jackson Hole.
Meadows variegated, and
Formations locally-derived
conglomerate;
persistent coal and
gray shale zone in
middle.
Paleocene
Unnamed 1,000-2,000 Sandstone and Eastern margin of
greenish-gray claystone, Jackson Hole.
and brown greenish-gray and
sandstone and brown,
claystone intertonguing at
sequence base with quartzite
pebble conglomerate.
Pinyon 500-5,000 Conglomerate, Eastern part of
Conglomerate brown, chiefly of Jackson Hole, Mt.
rounded quartzite; Leidy and Pinyon
coal and claystone Peak Highlands, and
locally at base. north end of Teton
Range.
[Illustration: Figure 45. _Pinyon Conglomerate of Paleocene age,
along the northwest margin of the Teton Range._]
During the early part of the Tertiary Period, mountain building and
basin subsidence were the dominant types of crustal movement. Seas
retreated southward down the Mississippi Valley and never again invaded
the Teton area. Environments on the recently uplifted land were diverse
and favorable for the development of new forms of plants and animals.
Rise and burial of mountains
The enormous section of Tertiary sedimentary rocks in the Jackson Hole
area (table 5) is one of the most impressive in North America. If the
maximum thicknesses of all formations were added, they would total more
than 6 miles, but nowhere did this amount of rock accumulate in a single
unbroken sequence. No other region in the United States contains a
thicker or more complete nonmarine Tertiary record; many areas have
little or none. The accumulation in Jackson Hole reflects active uplifts
of nearby mountains that supplied abundant rock debris, concurrent
sinking of nearby basins in which the sediments could be preserved, and
proximity to the great Yellowstone-Absaroka volcanic area, one of the
most active continental volcanic fields in the United States. The volume
and composition of the Tertiary strata are, therefore, clear evidence of
crustal and subcrustal instability.
[Illustration: Figure 46. _Teton region near end of deposition of
Paleocene rocks, slightly less than 60 million years ago. The
ancestral Teton-Gros Ventre uplift formed a partial barrier between
the Jackson Hole and Green River depositional basins; major
drainages from the Targhee uplift spread an enormous sheet of gravel
for 100 miles to the east. See figure 41 for State lines and
location map._]
The many thick layers of conglomerate are evidence of rapid erosion of
nearby highlands. The Pinyon Conglomerate (fig. 45), for example,
contains zones as much as 2,500 feet thick of remarkably well-rounded
pebbles, cobbles, and boulders, chiefly of quartzite identical with that
in the underlying Harebell Formation and derived from the same source,
the Targhee uplift. Like the Harebell the matrix contains small amounts
of gold and mercury. Rock fragments increase in size northwestward
toward the source area (fig. 46) and most show percussion scars,
evidence of ferocious pounding that occurred during transport by
powerful, swift rivers and steep gradients.
[Illustration: Figure 47. _Teton region at climax of Laramide
Revolution, between 50 and 55 million years ago. See figure 41 for
State lines and location map._]
Conglomerates such as the Pinyon are not the only clue to the time of
mountain building. Another type of evidence—faults—is demonstrated in
figure 16. The youngest rocks cut by a fault are always older than the
fault. Many faults and the rocks on each side are covered by still
younger unbroken sediments. These must, therefore, have been deposited
after fault movement ceased. By dating both the faulted and the
overlying unbroken sediments, the time of fault movement can be
bracketed.
Observations of this type in western Wyoming indicate that the Laramide
Revolution reached a climax during earliest Eocene time, 50 to 55
million years ago. Mountain-producing upwarps formed during this episode
were commonly bounded on one side by either reverse or thrust faults
(fig. 16B and 16C) and intervening blocks were downfolded into large,
very deep basins. The amount of movement of the mountain blocks over the
basins ranged from tens of miles in the Snake River, Salt River,
Wyoming, and Hoback Ranges directly south of the Tetons to less than 5
miles on the east margin of Jackson Hole (the west flank of the Washakie
Range shown in figure 1). The ancestral Teton-Gros Ventre uplift
continued to rise but remained one of the less conspicuous mountain
ranges in the region (fig. 47).
The Buck Mountain fault, the great reverse fault which lies just west of
the highest Teton peaks (see geologic map and cross section), was formed
either at this time or during a later episode of movement that also
involved the southwest margin of the Gros Ventre Mountains. The Buck
Mountain fault is of special importance because it raised a segment of
Precambrian rocks several thousand feet. Later, when the entire range as
we now know it was uplifted by movement along the Teton fault, the hard
basement rocks in this previously upfaulted segment continued to stand
much higher than those in adjacent parts of the range. All of the major
peaks in the Tetons are carved from this doubly uplifted block.
The brightly colored sandstone, mudstone, and claystone in the Indian
Meadows and Wind River Formations (lower Eocene) in the eastern part of
Jackson Hole were derived from variegated Triassic, Jurassic, and Lower
Cretaceous rocks exposed on the adjacent mountain flanks. Fossils in
these Eocene Formations show that it took less than 10 million years for
the uplifts to be deeply eroded and partially buried in their own
debris.
The Laramide Revolution in the area of Grand Teton National Park ended
during Eocene time between 45 and 50 million years ago, and as the
mountains and basins became stabilized a new element was added.
Volcanoes broke through to the surface in many parts of the
Yellowstone-Absaroka area and the constantly increasing volume of their
eruptive debris was a major factor in the speed of filling of basins and
burial of mountains throughout Wyoming. This entire process only took
about 20 million years, and along the east margin of Jackson Hole it was
largely completed during Oligocene time (fig. 48). However, east and
northeast of Jackson Lake a Miocene downwarp subsequently formed and in
it accumulated at least 7,000 feet of locally derived sediments of
volcanic origin.
[Illustration: Figure 48. _Teton region near the close of Oligocene
deposition, between 25 and 30 million years ago, showing areas of
major volcanoes and lava flows. See figure 41 for State lines and
location map._]
The First Big Lake
_Teewinot Lake_ (fig. 49), the first big freshwater lake in Jackson
Hole, was formed during Pliocene time, about 10 million years ago, and
in it the Teewinot Formation was deposited. These lake strata consist of
more than 5,000 feet of white limestone, thin-bedded claystone, and
_tuff_ (solidified ash made up of tiny fragments of volcanic rock and
splinters of volcanic glass). The claystones contain fossil snails,
clams, beaver bones and teeth, aquatic mice, suckers, and other fossils
that indicate deposition in a shallow freshwater lake environment. These
beds underlie Jackson Lake Lodge, the National Elk Refuge, part of
Blacktail Butte, and are conspicuously exposed in white outcrops that
look like snowbanks on the upper slopes along the east margin of the
park across the valley from the Grand Teton.
[Illustration: Figure 49. _Teton region near close of middle
Pliocene time, about 5 million years ago, showing areas of major
volcanoes and lava flows. See figure 41 for State lines and location
map._]
Teewinot Lake was formed on a down-faulted block and was dammed behind
(north of) a fault that trends east across the floor of Jackson Hole at
the south boundary of the park. Lakes are among the most short-lived of
earth features because the forces of nature soon conspire to fill them
up or empty them. This lake existed for perhaps 5 million years during
middle Pliocene time; it was shallow, and remained so despite the
pouring in of a mile-thick layer of sediment. This indicates that
downdropping of the lake floor just about kept pace with deposition.
[Illustration: Figure 50. _Restoration of a middle Eocene landscape
showing some of the more abundant types of mammals. Mural painting
by Jay H. Matterness; photo courtesy of the Smithsonian
Institution._]
_Uintatherium_ 6-horned, saber-toothed plant eater
_Stylinodon_ gnawing-toothed mammal
_Palaeosyops_ early titanothere
_Helaletes_ primitive tapir
_Sciuravus_ squirrel-like rodent
_Smilodectes_ lemurlike monkey
_Trogosus_ gnawing-toothed mammal
_Hyrachyus_ fleet-footed rhinoceros
_Ischyrotomus_ marmotlike rodent
_Homacodon_ even-toed hoofed animal
_Orohippus_ ancestral horse
_Patriofelis_ large flesh eater
_Mesonyx_ hyenalike mammal
_Helohyus_ even-toed hoofed mammal
_Metacheiromys_ armadillolike edentate
_Machaeroides_ saber-toothed mammal
_Hyopsodus_ clawed, plant-eating mammal
_Saniwa_ monitorlike lizard
_Crocodilus_ crocodile
_Echmatemys_ turtle
Other lakes formed in response to similar crustal movements in nearby
places. One such lake, _Grand Valley Lake_ (fig. 49), formed about 25
miles southwest of Teewinot Lake; both contained sediments with nearly
the same thickness, composition, appearance, age, and fossils. Although
these two lakes are on opposite sides of the Snake River Range, the
ancestral Snake River apparently flowed through a canyon previously cut
across the range and provided a direct connection between them.
Development of mammals
The Cenozoic Era is known as the “Age of Mammals.” Small mammals had
already existed, though quite inconspicuously, in Wyoming for about 90
million years before Paleocene time. Then about 65 million years ago
their proliferation began as a result of the extinction of dinosaurs,
obliteration of seaways that were barriers to distribution, and the
development of new and varied types of environment. These new
environments included savannah plains, low hills and high mountains,
freshwater lakes and swamps, and extensive river systems. The mammals
increased in size and, for the first time, became abundant in numbers of
both species and individuals. The development and widespread
distribution of grasses and other forage on which many of the animals
depended were highly significant. Successful adaptation of _herbivores_
(vegetation-eating animals) led, in turn, to increased varieties and
numbers of predatory _carnivores_ (meat-eating animals).
During early Eocene time, coal swamps formed in eastern Jackson Hole and
persisted for thousands of years, as is shown by 60 feet of coal in a
single bed at one locality. Continuing on into middle Eocene time, the
climate was subtropical and humid, and the terrain was near sea level.
Tropical breadfruits, figs, and magnolias flourished along with a more
temperate flora of redwood, hickory, maple, and oak. Horses the size of
a dog and many other small mammals were abundant. Primates, thriving in
an ideal forest habitat, were numerous. Streams contained gar fish and
crocodiles (fig. 50).
[Illustration: Figure 51. _A typical Oligocene landscape showing
some of the more abundant types of mammals. Mural painting by Jay H.
Matterness; photo courtesy of Smithsonian Institution._]
_Trigonias_ early rhinoceros
_Perchoerus_ early peccary
_Mesohippus_ 3-toed horse
_Aepinacodon_ remote relative of hippopotamus
_Archaeotherium_ giant piglike mammal
_Protoceras_ bizarre horned ruminant
_Hesperocyon_ ancestral dog
_Hyracodon_ small fleet-footed rhinoceros
_Poëbrotherium_ ancestral camel
_Hypisodus_ very small chevrotainlike ruminant
_Ictops_ small insect-eating mammal
_Brontotherium_ titanothere
_Protapirus_ ancestral tapir
_Glyptosaurus_ extinct lizard
_Hoplophoneus_ saber-toothed cat
_Subhyracodon_ early rhinoceros
_Merycoidodon_ sheeplike grazing mammal
_Hyaenodon_ archaic hyenalike mammal
_Hypertragulus_ chevrotainlike ruminant
Early in the Oligocene Epoch, between 30 and 35 million years ago, the
climate in Jackson Hole became cooler and drier, and the subtropical
plants gave way to the warm temperate flora of oak, beech, maple, alder,
and ash. The general land surface rose higher above sea level, perhaps
by accumulation of several thousand feet of Oligocene volcanic rocks
(fig. 52) rather than by continental uplift. _Titanotheres_ (large
four-legged mammals with the general size and shape of a rhinoceros)
flourished in great numbers for a few million years and then abruptly
vanished. Horses by now were about the size of a very small modern colt.
Rabbits, rodents, carnivores, tiny camels, and other mammals were
abundant in Jackson Hole, and the fauna, surprisingly, was essentially
the same as that 500 miles to the east, at a much lower elevation, on
the plains of Nebraska and South Dakota (fig. 51).
The Miocene Epoch (15 to 25 million years ago) was the time of such
intense volcanic activity in the Teton region that animals must have
found survival very difficult. A few skeletons and fragmentary parts of
camels about the size of a small horse and other piglike animals called
_oreodonts_ comprise our only record of mammals; nothing is known of the
plants. Farther east the climate fluctuated from subtropical to warm
temperate, gradually becoming cooler toward the end of the epoch.
Fossils in the Pliocene lake deposits (8 to 10 million years old; see
description of Teewinot Formation) include shallow-water types of
snails, clams, diatoms, and ostracodes, as well as beavers, mice,
suckers, and frogs. Pollen in these beds show that adjacent upland areas
supported fir, spruce, pine, juniper, sage, and other trees and shrubs
common to the area today. Therefore, the climate must have been much
cooler than in Miocene time. No large mammals of Pliocene age have been
found in Jackson Hole. The record of life during Quaternary time is
discussed later.
[Illustration: Figure 52. _Layers of volcanic conglomerate separated
by thin white tuff beds in Wiggins Formation. These cliffs, on the
north side of Togwotee Pass, are about 1,100 feet high and represent
a cross section of part of the enormous blanket of waterlaid debris
that spread south and east from the Yellowstone-Absaroka volcanic
area. These and younger deposits from the same general source filled
the basins and almost completely buried the mountains in this part
of Wyoming._]
Volcanoes
Volcanoes are one of the most interesting parts of the geologic story of
the Teton region. Although ash from distant volcanoes had settled in
northwestern Wyoming at least as far back in time as Jurassic, the first
nearby active volcanoes (since the Precambrian) erupted in the
Yellowstone-Absaroka region during the early Eocene, about 50 million
years ago. From then on, the volcanic area grew in size and the violence
of eruptions and volume of debris increased until Pliocene time. This
debris had a profound influence on the color and composition of the
sediments and on the environment and types of plants and animals.
The color of the volcanic rocks and the sediments derived from them
varies significantly from one epoch to another. For example, the middle
Eocene rocks are white to light-green, red, and purple, upper Eocene are
dark-green, Oligocene are light-gray, white, and brown, Miocene are
dark-green, brown, and gray, and Pliocene are white to red-brown.
[Illustration: Figure 53. _Air oblique view south, showing the north
end of the Teton Range disappearing beneath Pleistocene lava flows.
Light-colored bare area at lower left is vertical Paleozoic
limestone surrounded on three sides by nearly horizontal rhyolite
lava flows. Bare slope at lower right is west-dipping Pinyon
Conglomerate, also overlapped by lava. Grand Teton is on right
skyline and Mt. Moran is rounded summit on middle skyline._]
As mentioned earlier, it is probable that the vast outpouring of
volcanic rocks during late Tertiary time in the Teton region and to the
north and northeast is directly related to the subsidence of Jackson
Hole and the rise of the Tetons.
The spectacular banded cliffs of the Wiggins Formation on both sides of
Togwotee Pass (fig. 52) and farther north in the Absaroka Range are
remnants of Oligocene volcanic conglomerate and tuff that once spread as
a blanket several thousand feet thick across eastern Jackson Hole and
partially or completely buried the nearby older folded mountain ranges.
[Illustration: Figure 54. _Obsidian, a volcanic glass less than 10
million years old, especially prized by Indians who used it for
spear and arrow points and for tools._]
About 25 million years ago, with the start of the Miocene Epoch,
volcanic vents opened up within, and along the borders of, Grand Teton
National Park. Major centers of eruption were at the north end of the
Teton Range, east of Jackson Lake, and south of Spread Creek. They
emitted a prodigious amount of volcanic ash and fragments of congealed
lava. For example, adjacent to one vent a mile in diameter, about 4
miles north-northeast of Jackson Lake Lodge, is a continuous section,
7,000 feet thick, of waterlaid strata derived in large part from this
volcanic source. These sedimentary rocks comprise the Colter Formation
which is darker colored and contains more iron and magnesium than the
Wiggins Formation. The site of deposition at this locality was a
north-trending trough that represented an early stage in the downwarping
of Jackson Hole.
Pliocene volcanoes erupted in southern and central Yellowstone Park. The
volcanoes emitted viscous, frothy, pinkish-gray and brown lava called
_rhyolite_. This is an extrusive igneous rock that has the same
composition as granite, but is much finer grained. In several places,
lava apparently flowed into the north end of Teewinot Lake, chilled
suddenly, and solidified into a black volcanic glass called _obsidian_.
Because it chips easily into thin flakes having a smooth surface,
obsidian was prized by the Indians, who used it for spear and arrow
points (fig. 54). Some of this obsidian has a potassium-argon date of 9
million years.
[Illustration: Figure 55. _East face of Signal Mountain showing
Bivouac Formation (upper Pliocene or Pleistocene). Tilted ledge is
rhyolitic welded tuff 2.5 million years old, and slopes above and
below it are conglomerate. National Park Service photo by W. E.
Dilley._]
After Teewinot Lake was filled with sediment, the floor of Jackson Hole
became a flat boulder-covered surface. Nearby vents erupted heavy fiery
clouds of gaseous molten rock that rolled across this plain and then
congealed into hard layers with the general appearance of lava flows.
Under a microscope, however, the rock is seen to be made up of
compressed fragments of glass that matted down and solidified when the
clouds stopped moving. This kind of rock is called a _welded tuff_. One
of these forms the conspicuous ledge in the Bivouac Formation on the
north and east sides of Signal Mountain (fig. 55), and is especially
important because it has a potassium-argon date of 2.5 million years.
More of this _welded tuff_ flowed southward from Yellowstone National
Park, engulfed the north end of the Teton Range (fig. 53), and continued
southward along the west side of the mountains for 35 miles and along
the east side for 25 miles.
[Illustration: Figure 56. _The final 3 million years on our
yardstick of time, enlarged to show approximate dates of major
events._]
THE LAST HUNDREDTHS ABSOLUTE TIME IMPORTANT EVENTS
OF AN INCH OF THE (Years ago)
YARDSTICK
0 0 Last glaciation followed by
faulting
¹/₁₀₀₀ 50000 Second glaciation
²/₁₀₀₀ 100000 ?—First glaciation
⁶/₁₀₀₀ 700000 ?—Second Quaternary lake
⁸/₁₀₀₀ 1 million ?—Tilting and faulting of
southern part of Jackson Hole
¹¹/₁₀₀₀ 1.3 million ?—First Quaternary lake
¹²/₁₀₀₀ 1.5 million } Complex series of volcanic
eruptions in southern Jackson
Hole
¹⁵/₁₀₀₀ 1.9 million }
¹⁶/₁₀₀₀ 2 million ?—Development of Hoback
normal fault
²/₁₀₀ 2.5 million Eruption of welded tuff in
Bivouac Formation
²⁴/₁₀₀₀ 3 million
QUATERNARY—TIME OF ICE, MORE LAKES, AND CONTINUED CRUSTAL DISTURBANCE
The Quaternary Period is represented by less than 15-thousandths of the
last inch on our yardstick of time (fig. 56) and the entire Ice Age
takes up less than 2-thousandths of an inch (less than the thickness of
this page). Nevertheless, the spectacular effects of various forces of
nature on the Teton landscape during this short interval of time are of
such significance that they warrant a separate discussion. The role of
glaciers in carving the rugged Teton peaks and shaping the adjacent
valleys was mentioned in the first part of this booklet, but is
discussed in more detail here. The magnitude and complexity of crustal
movements increased during the final 2 million years of time—so much so
that the beginning of Quaternary time has not yet been identified with
any single event. Figure 56 shows the major events described below.
Hoback normal fault
The _Hoback normal fault_, 30 miles long, with a mile or more
displacement, developed in the southernmost part of Jackson Hole about 2
million years ago. This fault is on the east side of the valley. Thus,
the valley block was downdropped between this fault and the Teton fault
that borders the west side.
Volcanic activity
During or shortly after major movement on the Hoback fault, and perhaps
related to it, there was a complex series of volcanic eruptions west and
north of the town of Jackson, along the south boundary of the park. In
rapid succession, lavas of many types, with a combined thickness of more
than 1,000 feet, were extruded and volcanic plugs intruded into the
near-surface sedimentary rocks. These volcanic rocks can be seen on the
East and West Gros Ventre Buttes.
There are no active volcanoes in the Teton region today and no
postglacial lava flows or cinder cones. Five miles north of Grand Teton
National Park are boiling springs (Flagg Ranch hot springs) that are
associated with the youngest (late Quaternary) lavas in southern
Yellowstone Park. Elsewhere in Jackson Hole are a number of lukewarm
springs but their relation to volcanic rocks has not been determined.
What happened to the vast thicknesses of volcanic debris? We know they
existed because sections of them have been measured on the eroded edges
of uptilted folds and fault blocks. Many cubic miles of these rocks are
now buried beneath the floor of Jackson Hole, but a much greater volume
was carried completely out of the region by water, ice, and wind during
the final chapter of geologic history.
Preglacial lakes
Remnants of two sets of lake deposits in Jackson Hole record preglacial
events in Quaternary time. Downdropping of southern Jackson Hole along
the Hoback and Teton faults blocked the southwestward drainage of the
Snake River, and a new lake formed overlapping and extending south of
the site of the long-vanished Teewinot Lake. Incorporated in the lake
sediments are fragments of lava like that in nearby Quaternary flows.
From this we know that the lake formed after at least some of the lava
was emplaced. Apparently subsidence was more rapid than filling, for a
time, at least, because this new lake was deep. Fossil snails preserved
in olive-drab to gray fine-grained claystone overlying lava flows at the
north end of East Gros Ventre Butte are the kind now living at depths of
120 to 300 feet in Lake Tahoe, California-Nevada. Near the margins of
the lake, pink and green claystone and soft sandstone were deposited.
The duration of this lake is not known but it lasted long enough for 200
feet of beds to accumulate. Subsequent faulting and warping destroyed
the lake, left tilted remnants of the beds perched 1,000 feet up on the
east side of Jackson Hole, and permitted the Snake River to reestablish
its course across the mountains to the southwest.
Later downdropping of Jackson Hole impounded a second preglacial lake.
Little is known about its extent because nearly everywhere the soft
brown and gray shale, claystone, and sandstone deposited in it were
scooped out and washed away during subsequent glaciations. A few
remnants of the lake deposits are preserved in protected places,
however; two are within the Gros Ventre River Valley—one downstream from
Lower Slide Lake about a mile east of the park and the other 4 miles
farther east. The latter remnant is nearly 500 feet thick and the upper
half is largely very fine grained shale and claystone. This fine texture
suggests that the lake existed for a good many thousand years, for such
deposits commonly accumulate more slowly than coarser grained debris.
[Illustration: Figure 57. _Map showing extent and direction of
movement of first and largest ice sheet. See figure 41 for State
lines and location map._]
The Ice Age
With the uplift of the Teton Range and the formation of Jackson Hole
late in Cenozoic time the landscape gradually began to assume the
general outlines that we see today. Rain, wind, snow, and frost shaped
the first crude approximations of the present ridges and peaks. Streams
cut into the rising Teton fault block, eroding the ancestral canyons
deeper and deeper as the uplift continued. The most recent great chapter
in the story of the Teton landscape, however, remained to be written by
the glaciers of the _Ice Age_.
The reasons for the climatic changes that caused the Ice Age are still a
matter of much scientific debate. Various theories have been advanced
that attribute them to changes in solar radiation, changes in the
earth’s orbit and inclination to the sun, variations in the amount of
carbon dioxide in the atmosphere, shifts in the positions of the
continents or the poles, and to many other factors, but none has met
with universal acceptance. No doubt the explanation lies in some unusual
combination of circumstances, for widespread glaciation occurred only
twice before in the earth’s history—once in the late Precambrian and
once during the Permian. It is quite clear, however, that the glaciers
did not form in response to any local cause such as the uplift of the
Teton Range, for concurrent climatic changes and ice advance took place
throughout many parts of the world.
At least three times in the last 250,000 years glaciers from the
surrounding highlands invaded Jackson Hole. The oldest and most
widespread glaciation probably took place about 200,000 years ago; it
was called the _Buffalo Glaciation_ by Prof. Eliot Blackwelder in 1915
(see selected references). The age estimate is based on measurements of
the thickness of the decomposed layer on the surface of obsidian pebbles
in the glacial debris. Major sources of ice were the Beartooth Mountains
(fig. 1), the Absaroka Range, and the Wind River Range. The Gros Ventre
Mountains and Teton Range furnished lesser amounts of ice.
The ice from the Beartooth and Absaroka centers of ice accumulation
converged in the northeastern part of Grand Teton National Park and
flowed south along the face of the Teton Range in a giant stream that in
many places was 2,000 feet thick (fig. 57). All but the highest parts of
the Pinyon Peak and Mount Leidy Highlands were buried and scoured.
Signal Mountain, Blacktail Butte, and the Gros Ventres Buttes were
overridden and shaped by ice at this time. Another glacier, this one
from the Wind River Range, flowed northwest along the Continental
Divide, then down the Gros Ventre River Valley, and merged with the
southward-moving main ice stream west of Lower Slide Lake. Where Jackson
Hole narrows southward, the glacier became more and more confined, but
nevertheless flowed all the way through the Snake River Canyon and on
into Idaho.
[Illustration: Figure 58. _Glacial deposits, outwash, and loess
exposed along Boyle Ditch in Jackson Hole National Elk Refuge.
Indicated are middle Pliocene Teewinot formation (A), oldest till
(B), Bull Lake outwash gravel (C), and post-Bull Lake loess (D),
which here contains snail shells dated by Carbon-14 as 15,000 years
old. Height of cliff is about 30 feet._]
The volume of this great ice mass was probably considerably more than
1,000 cubic miles. When it melted, nearly all the previously accumulated
soil in Jackson Hole was washed away and a pavement of quartzite
boulders mantled much of the glaciated surface. In areas not
subsequently glaciated, the lack of soil and abundance of quartzite
boulders drastically influenced the topography, later drainage,
distribution of all types of vegetation, especially conifers and grass,
and the pattern of human settlement and industry.
[Illustration: Figure 59. _View west from the Snake River overlook
showing at upper right the Burned Ridge moraine (with trees) merging
southward with the highest (oldest) Pinedale outwash plain. The next
lower surface is composed of outwash from the Jackson Lake moraine
which lies to the right, out of the picture. At the bottom is
Deadman’s Bar, a gravel deposit at the present river level. Photo by
H. D. Pownall._]
The second glaciation, named _Bull Lake_, was less than half as
extensive as the first. A large tongue of ice from the Absaroka center
of accumulation flowed down the Buffalo River Valley and joined ice from
the Tetons on the floor of Jackson Hole. An enormous outwash fan of
quartzite boulders extended from near Blacktail Butte southward
throughout most of southern Jackson Hole. Glaciers in the Gros Ventre
Mountains did not advance beyond the east margin of the valley floor.
Carbon-14 ages and data from weathered obsidian pebbles suggest that
this glaciation took place between 35,000 and 80,000 years ago.
Bull Lake moraines and outwash deposits are overlain directly in the
southern part of Jackson Hole by fine silt, rather than by deposits of
the third glaciation (fig. 58). This silt, of windblown origin, is
called _loess_ and contains fossil shells dated by Carbon-14 as between
13,000 and 19,000 years old. Wherever the loess occurs, it is marked by
abundant modern coyote dens and badger burrows.
[Illustration: Figure 60. _Air oblique view west toward the Teton
Range, showing effects of Pinedale Glaciation on the landscape. Mt.
Moran is at top left; the mountain front is broken by U-shaped
valleys from which ice emerged into the area now occupied by Jackson
Lake. The timbered area bordering Jackson Lake is the Jackson Lake
moraine. One of the braided outlet channels breaching the Jackson
Lake moraine can be seen crossing the outwash plain at the left
center. Lakes at lower right occupy “potholes” near where the
9,000-year-old snail shells occur. Snake River is in foreground.
Photo by R. L. Casebeer._]
The third and last glaciation, named the _Pinedale_, was even less
extensive than the others. Nevertheless it was of great importance for
it added the final touches to the present landscape. The jagged
intricately ice-carved peaks (fig. 4) and the glittering lakes and broad
gravelly plains are vivid reminders of this recent chapter in geologic
history.
Pinedale glaciers advanced down Cascade, Garnet, Avalanche, and Death
Canyons and spilled out onto the floor of Jackson Hole, where they built
the outermost loops of the conspicuous terminal moraines that now
encircle Jenny, Bradley, Taggart, and Phelps Lakes (fig. 13). Ice
streams from Glacier Gulch and Open Canyon also left prominent moraines
on the valley floor, but these do not contain lakes. Ice from Leigh
Canyon and all of the eastward-draining valleys to the north combined to
form a large glacier in roughly the present position of Jackson Lake.
This ice entirely surrounded Signal Mountain, leaving only the upper few
hundred feet projecting as an island or _nunatak_.
[Illustration: Figure 61. _The Pinedale Glaciers in the central part
of Jackson Hole as they might have appeared at the time the Jackson
Lake moraine was built. Solid color areas are lakes; dark irregular
pattern shows areas of moraine deposited during the maximum advance
of the Pinedale Glaciers. Pattern of open circles shows older
Pinedale outwash plains; pattern of fine dots shows outwash plains
built at the time the glaciers were in the positions shown in the
drawing. Coarser dots near the margins of the glaciers represent
concentrations of rock debris in the ice._]
The southernmost major advance of Pinedale ice from Jackson Lake is
marked by a series of densely timbered moraines that cross the Snake
River Valley. This series is collectively named the _Burned Ridge
moraine_ (fig. 61). Extending southward for 10 miles from this moraine
is a remarkably flat surfaced gravelly outwash deposit. It was spread by
streams that poured from the glacier at the time the moraine was being
built (fig. 59). East of the Snake River, the main highway from a point
just north of Blacktail Butte to the Snake River overlook is built on
this flat untimbered surface. We assume that the outwash is younger than
15,000 years because it apparently overlies loess of that age.
The glacier withdrew rapidly northward from the Burned Ridge moraine,
leaving behind many large irregular masses of stagnant, debris-covered
ice. The sites of these became kettles, locally known as “The Potholes”
(fig. 12). The main glacier retreated to a position marked by the loop
of moraines just south of Jackson Lake (fig. 60). Figure 61 is a sketch
map showing how the glaciers in this part of Jackson Hole might have
appeared at the time the Jackson Lake moraine was built.
Abundant snail shells have been found in lake sediments in the bottoms
of the kettles north of the Burned Ridge moraine (fig. 60) as well as on
low ridges between them. Carbon-14 age determinations indicate that the
snails lived about 9,000 years ago, either in a lake already present
before the Pinedale ice advanced and formed the Burned Ridge moraine or
in ponds that filled kettles left as the ice melted behind this moraine.
In either case, the shells indicate that the Pinedale glaciers probably
existed on the floor of Jackson Hole as recently as 9,000 years ago, at
a time when Indians were already living in the area. We can easily
imagine the fascination with which these primitive peoples may have
watched as year after year the glaciers wasted away, slowly retreating
back into the canyons, then withdrawing into the sheltered recesses of
the high mountains, eventually to dwindle and disappear.
Many bits of evidence, both from North America and Europe, indicate that
there was a period called the _climatic optimum_ about 6,000 years ago
when the climate was significantly warmer and drier than at present. We
suspect, though there is as yet no direct proof, that the Pinedale
glaciers wasted away entirely during this interval.
The modern pattern of vegetation in Jackson Hole is strongly influenced
by the distribution of Pinedale glacial moraines and outwash deposits.
Almost without exception the moraines are heavily forested, whereas the
nearby outwash deposits are covered only by a sparse growth of
sagebrush. This is probably because the moraines contain large amounts
of clay and silt produced by the grinding action of the glaciers.
Material of this type retains water much better and, because of the
greater variety of chemical elements, is more fertile than the porous
quartzite gravel and sand on the outwash plains.
Modern glaciers
About a dozen small rapidly dwindling glaciers exist today in shaded
reentrants high in the Teton Range. They are probably vestiges of ice
masses built up since the climatic optimum, during the so-called
“_Little Ice Age_.” These glaciers, while insignificant compared to
those still present in many other mountain ranges, are fascinating
working models of the great ice streams that shaped the Tetons during
Pleistocene time.
The Teton Glacier (fig. 6) is one of the best known. It is an ice body
about 3,500 feet long and 1,100 feet wide that lies at the head of
Glacier Gulch, shaded by the encircling ridges of the Grand Teton, Mount
Owen, and Mount Teewinot. Ice in the central part is moving at a rate of
more than 30 feet a year.
THE PRESENT AND THE FUTURE
The geologic story of the Teton country from the time the earth was new
to the present day has been summarized. What can we learn from it? We
become aware that events recorded in the rocks are not a chaotic jumble
of random accidents but came in an orderly, logical succession. We see
the majestic parade of life evolving from simple to complex types,
overcoming all natural disasters, and adapting to ever-changing
environments. We can only speculate as to the motivating force that
launched this fascinating geologic and biologic venture and what the
ultimate goal may be. New facts and new ideas are added to the story
each year, but many unknown chapters remain to be studied; these offer
an irresistible, continuing challenge to inquisitive minds, strong
bodies, and restless, adventurous spirits.
Most geologic processes that developed the Teton landscape have been
beneficial to man; a few have interfered with his activities, cost him
money, time, effort, and on occasion, his life. Postglacial faulting and
tilting along the southern margin of Grand Teton National Park diverted
drainage systems (such as Flat Creek, southwest of the Flat Creek fault
on the south edge of the geologic map), raised hills, dropped valleys,
and made steep slopes unstable. Flood-control engineers wage a
never-ending struggle to keep the Snake River from shifting to the west
side of Jackson Hole as the valley tilts westward in response to
movement along the Teton fault. Each highway into Jackson Hole has been
blocked by a landslide at one time or another and maintenance of roads
across slide areas requires much ingenuity. We see one slide (the Gros
Ventre) that blocked a river; larger slides have occurred in the past,
and more can be expected. Abundant fresh fault scarps are a constant
reminder that public buildings, campgrounds, dams, and roads need to be
designed to withstand the effects of earthquakes. Some of these problems
have geologic solutions; others can be avoided or minimized as further
study increases our understanding of this region.
Man appeared during the last one-fiftieth of an inch on our yardstick of
time gone by. In this short span he has had more impact on the earth and
its inhabitants than any other form of life. Will he use wisely the
lessons of the past as a guide while he writes his record on the
yardstick of the future?
APPENDIX
Acknowledgements
This booklet could not have been prepared without the cooperation and
assistance of many individuals and organizations. We are indebted to the
National Park Service for the use of facilities, equipment, and
photographs, and for the enthusiasm and interest of all of the park
staff. We especially appreciate the cooperation, advice, and assistance
rendered by the late Fred C. Fagergren, former superintendent of Grand
Teton National Park; Willard E. Dilley, former chief park naturalist;
and R. Alan Mebane, former assistant chief park naturalist.
Profs. Charles C. Bradley and John Montagne of Montana State University
and Bruno J. Giletti of Brown University generously provided us with
unpublished data. Cooperators during the years of background research
were the late Dr. H. D. Thomas, State Geologist of Wyoming, and Dr. D.
L. Blackstone, Jr., Chairman, Department of Geology, University of
Wyoming.
Helpful suggestions were made by many of our colleagues with the U. S.
Geological Survey; S. S. Oriel, in particular, gave unstintingly of his
time and talents in the review and revision of an early version of the
manuscript. A later version had the further benefit of critical review
by three other people, all experienced in presenting various types of
scientific data to public groups: John M. Good, former chief park
naturalist of Yellowstone National Park; Bryan Harry, former assistant
chief park naturalist of Grand Teton National Park; and Richard Klinck,
“1965 National Teacher of the Year.”
We are indebted to Ann C. Christiansen, Geologic Map Editor, for advice
and guidance on the illustrations and to R. C. Fuhrmann and his staff
for preparation of many of the line drawings. Block diagrams and photo
artwork were prepared by J. R. Stacy and R. A. Reilly. All photographs
without specific credit lines are by the authors. From the beginning of
the Teton field study to editing and proofing of the final manuscript,
our wives, Jane M. Love and Linda H. Reed, have been enthusiastic and
indispensable participants.
Selected references—if you wish to read further
Blackwelder, Eliot, 1915, Post-Cretaceous history of the mountains of
central western Wyoming: Jour. Geology, v. 23, p. 97-117,
193-217, 307-340.
Bradley, F. H., 1873, Report on the geology of the Snake River
district: U.S. Geol. Survey Terr. 6th Ann. Rept. (Hayden), p.
190-271.
Edmund, R. W., 1951, Structural geology and physiography of the
northern end of the Teton Range, Wyoming: Augustana Library
Pub. 23, 82 p.
Fryxell, F. M., 1930, Glacial features of Jackson Hole, Wyoming:
Augustana Library Pub. 13, 129 p.
——, 1938, The Tetons, interpretations of a mountain landscape: Univ.
California Press, Berkeley, Calif., 77 p.
Hague, Arnold, 1904, Atlas to accompany U.S. Geol. Survey Monograph 32
on the geology of Yellowstone National Park.
——, Iddings, J. P., Weed, W. H., and others, 1899, Geology of the
Yellowstone National Park: U.S. Geol. Survey Monograph 32, Pt.
2, 893 p.
Harry, Bryan, 1963, Teton trails, a guide to the trails of Grand Teton
National Park: Grand Teton Natural History Association, Moose,
Wyo., 56 p.
Horberg, Leland, 1938, The structural geology and physiography of the
Teton Pass area, Wyoming: Augustana Library Pub. 16, 86 p.
Hurley, P. M., 1959, How old is the earth?: Anchor Books, Garden City,
N. Y., 160 p.
Ortenburger, Leigh, 1965, A climber’s guide to the Teton Range: Sierra
Club, San Francisco, 336 p.
St. John, O. H., 1883, Report on the geology of the Wind River
district: U.S. Geol. Geog. Survey Terr. 12th Ann. Rept.
(Hayden), Pt. 1, p. 173-270.
Wyoming Geological Association, 1956, Guidebook, 11th annual field
conf., Jackson Hole, Wyoming, 1956, Casper, Wyo., 256 p.,
incl. sketch maps, diagrams, tables, and illus., also geol.
map, sections, and charts. Composed of a series of individual
papers by various authors.
About the authors
J. D. Love, a native of Wyoming, received his bachelor and master of
arts degrees from the University of Wyoming and his doctor of philosophy
degree from Yale University. His first field season in the Teton
country, in 1933, was financed by the Geological Survey of Wyoming.
After 12 years of geologic work ranging from New England to Utah and
Michigan to Mississippi, he returned to the Teton region. Beginning in
1945, he spent parts or all of 20 field seasons in and near the Tetons.
He compiled the first geologic map of Teton County. He is the senior
author of the geologic map of Wyoming, and author or co-author of more
than 70 other published maps and papers on the geology of Wyoming. In
1961, the University of Wyoming awarded him an honorary doctor of laws
degree for his work on uranium deposits that “led to the development of
the uranium industry in Wyoming.” The Wyoming Geological Association
made him an honorary life member and gave him a special award for his
geologic studies of the Teton area. He is a Fellow of the Geological
Society of America and is active in various other geological
organizations, as well as having been president of the Wyoming Chapters
of Sigma Xi (scientific honorary) and Phi Beta Kappa (scholastic
honorary) societies.
John C. Reed, Jr., joined the U.S. Geological Survey in 1953 after
receiving his doctor of philosophy degree from the John Hopkins
University. His principal geologic work before coming to the Teton
region was in Alaska and in the southern Appalachians. Beginning in
1961, he spent five field seasons studying and mapping the Precambrian
rocks in Grand Teton National Park, including all the high peaks in the
Teton Range. He is a noted mountaineer, a Fellow of the Geological
Society of America, a member of the Arctic Institute of North America,
and the American Alpine Club. His numerous publications, in addition to
those on the Tetons, describe the geology of mountainous areas in
Alaska, the Appalachians, and Utah.
Index of selected terms and features
_Term_ _Defined or described on page_
A
amphibolite 51
anticlines 85
B
badlands 14
bentonite 81
biotite 51
brachiopods 70
Buffalo Glaciation 106
Bull Lake Glaciation 108
Burned Ridge moraine 111
buttes 18
C
Carbon-14 48
carnivores 95
chlorite 56
cirque 30
climatic optimum 112
Cordilleran trough 69
D
diabase 59
dikes 56
dipping 39
dolomite 75
E
“edgewise” conglomerate 73
epochs 46
eras 46
erosion 27
erratics 31
extrusive igneous rocks 46
F
fault 9
fault block mountain range 37
fault scarps 37
formations 66
frost wedging 25
G
geologic 10
glacial striae 30
gradients 28
Grand Valley Lake 95
granite 55
granite gneiss 54
groups 47
gypsum 79
H
herbivores 95
Hoback normal fault 103
hole 8
hornblende 51
I
Ice Age 105
igneous rocks 46
intrusive igneous rocks 46
J
Jackson Hole 8
jade 55
K
kettle 31
L
Laramide Revolution 82
lateral moraine 30
layered gneisses 51
Little Ice Age 112
loess 108
M
magma 60
magnetite 52
marine sedimentary rocks 21
metamorphic rocks 53
muscovite 55
N
normal fault 39
nunatak 111
O
obsidian 101
oreodonts 97
outwash 31
outwash plain 31
outwash terraces 34
P
pegmatite 56
period 46
Pinedale Glaciation 109
Q
quartzite 63
R
reverse fault 39
rhyolite 100
rock glaciers 26
S
schist 51
sedimentary rocks 45
series 47
serpentine 55
“soapstone” 55
Sundance Sea 79
systems 46
T
talus 24
Targhee uplift 83
Teewinot Lake 92
terminal moraine 30
Tetons 8
Teton fault 37
thrust fault 39
timberline 15
titanothere 97
treeline 15
Triceratops 85
trilobites 70
tuff 92
W
welded tuff 101
The GRAND TETON NATURAL HISTORY ASSOCIATION
The Grand Teton Natural History Association assists the National Park
Service in the development of a broad public understanding of the
geology, plant and animal life, history, and related subjects pertaining
to Grand Teton National Park. It aids in the development of museums and
wayside exhibits, offers for sale publications on natural and human
history, and cooperates with the Government in the interest of Grand
Teton National Park.
_Mail orders_: For a publication list, write the Grand Teton Natural
History Association, Moose, Wyoming 83012.
_Creative Director_: Century III Advertising. Inc.
_Designer_: Les Hays Studios, Inc.
_Color Separations_—_Assembly_—_Plates_: Orent Graphic Arts, Inc.
_Type_: Bodoni and Gothic
_Printer_: Omaha Printing Co.
_Printing_: Offset Lithography.
Six Colors on Covers
Two Colors on Body
[Illustration: GEOLOGIC MAP OF GRAND TETON NATIONAL PARK]
[Illustration: EXPLANATION]
CENOZOIC
QUATERNARY
Sand, gravel, and talus
_Includes glacial outwash and materials deposited by present
streams_
Landslide deposits
Moraine deposits of Pinedale glaciers
Moraine deposits of Bull Lake and older glaciers
TERTIARY
Volcanic rocks
_Lava flows and volcanic ash_
Conglomerate, sandstone, shale, claystone, marl, and pumice
_Deposited on land or in shallow lakes_
MESOZOIC
Conglomerate, sandstone, shale, and coal
_Deposited on land_
Shale, sandstone, and limestone
_Mostly deposited in shallow seas_
PALEOZOIC
Limestone, shale, and sandstone
_Deposited in shallow seas_
PRECAMBRIAN
Diabase dikes
Granite, gneiss, and schist
Fault
_Dashed where approximately located; dotted where concealed beneath
unfaulted younger deposits. U is on the side that moved up; D,
on the side that moved down_
Geologic contact
[Illustration: View southwest from Lake Solitude toward the Grand
Teton (right), Mt. Owen, and Mt. Teewinot. _Wyoming Travel
Commission photo by J. R. Simon._]
[Illustration: Grand Teton, Mt. Owen, and Mt. Teewinot from Jenny
Lake Flat. _National Park Service photo by W. E. Dilley._]
Transcriber’s Notes
—Retained publication information from the printed edition: this eBook
is public-domain in the country of publication.
—Corrected a few palpable typos.
—Re-arranged text in captions closer to the corresponding image.
—Expanded ambiguous references to illustrations, _e.g._ “Figure D” to
“Figure 16D”
—Added one section heading, “The First Big Lake” to match the table of
contents.
—Included a transcription of the text within some images, with estimated
scale readings from charts.
—In the text versions only, text in italics is delimited by
_underscores_.
End of the Project Gutenberg EBook of Creation of the Teton Landscape, by
J. D. Love and John C. Reed
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