Grand Teton

National Park

Wyoming

Grand Teton National Park, Wyoming

Geologic structures in Grand Teton National Park are located within the Middle Rocky Mountain physiographic province and result from tectonic activities associated with the Laramide orogeny and continuing through recent times. In the southern Yellowstone area, thehigh-altitude Two Ocean Plateau was created by rhyolite flows of Quaternary age (Love and Reed, 1968; Love and Christiansen, 1985). The Washakie and Absaroka ranges are located northeast of the park and consist of thrustfaulted, asymmetric anticlines and andesitic volcaniclastic rocks, respectively. The Pinyon Peak and Mount Leidy Highlands, east of the park, include conglomerates of late Cretaceous and early Tertiary age. The Gros Ventre Range, located southeast of the park, is composed of thrust faulted sedimentary rocks of Mesozoic and Paleozoic age, including carboniferous units which form karst. The Teton Range is an upthrown, tilted fault-block that contains more than 5,000 feet of Paleozoic sedimentary strata including significant deposits of karst forming limestones and dolomites. Jackson Hole is a structural basin as much as 3.1 miles deep formed by a tilted, downthrown fault block hinged to the east (Nolan and Miller, 1995). Rocks ranging in age from Precambrian to Quaternary crop out in and near Grand Teton National Park. The Teton Range consists of a core of igneous and metamorphic Precambrian rocks overlain in most of the range by westward dipping sedimentary Paleozoic rocks. Jackson Hole contains mostly Quaternary glacial, lacustrine, and alluvial deposits underlain by Tertiary volcanics and older rocks, forming a sequence as much as 4,000 - 7,000 feet thick. The uplands east of Jackson Hole are underlain by Precambrian through Cenozoic rock strata (Cox, 1974; Nolan and Miller, 1995). Alluvium occurs as flood plain deposits and alluvial fans in valleys, and commonly consists of well-sorted beds of silt, sand, and gravel. Much of the alluvium is glacial-outwash material that has been reworked by modern streams and greatly resembles the parent material. Alluvial fans have formed along the margins of Jackson Hole where streams enter the valley from surrounding uplands. Relatively large amounts of ground water occur within the alluvium of the park (Cox, 1974). Faults have greatly altered the continuity of rock units in and near the park. Vertical displacement along the Teton Fault is as much as 23,000 feet (4.4 miles). Faults are also present east and south of Jackson Hole, but are obscured by glacial and alluvial deposits in Jackson Hole (Cox, 1974). Jackson Hole and the bordering Tetons are both tilted blocks of the earth's crust. The block forming the Tetons was uplifted on its east side, while the block forming Jackson Hole was down dropped on its west side. These blocks are joined at the Teton Fault, and the floor of Jackson Hole tilts westward toward the Tetons. Relative movement along the fault is estimated to average about 1 foot per 300 - 400 years. As tilting of the block continues, the Snake River seeks the lowest portion of the valley by migrating westward. Flood-control levees, within and south of the park, inhibit this natural migration (Love and Reed, 1968). Jackson Hole has been glaciated at least three times, with the oldest event being the most widespread. The ice in many places exceeded 2,000 feet in thickness, and later glacial events eroded or covered parts of earlier ones (Love and Reed, 1968). During the latest glacial stage, ice flowed down canyons in the Teton Range onto the floor of Jackson Hole and built the moraines that dam Jackson, Leigh, Jenny, Bradley, Taggart, and Phelps lakes. The glacial deposits are generally either morainal or outwash deposits consistent with alpine glaciation. Morainal deposits are commonly ridges or hills that were formed by material deposited directly by glaciers as the ice melted. Outwash deposits form plains where material carried by streams, that flowed from the melting glaciers, was deposited. Outwash deposits are more permeable and yield water more easily to wells than morainal deposits. Wells yielding 1,000 gpm can be completed in the outwash deposits of Jackson Hole. Morainal deposits contain more clay and silt than outwash deposits resulting in better retention of soil moisture and nutrients. Consequently, moraines are heavily forested, while outwash plains are covered by sagebrush (Cox, 1974). Lacustrine deposits in and near the park occur where lakes existed before, during, or after glaciation. Landslide deposits also occur, most extensively in the upland areas east and northeast of Jackson Hole (Cox, 1974). The Gros Ventre drainage is characterized by sedimentary terrain in which numerous landslides have occurred. The mass wasting contributes large volumes of bedload to streams draining from the east (Wyoming State Engineer's Office,1972).

SOILS

The variety of soils found in the area result from the kinds and origins of the parent materials as well as variations in climatic conditions. There are three predominant soil types, the most widespread of which is a loamy to loamy-skeletal mixed soil found from 6,000 to 12,500 feet on low mountains, fans, and uplands. Generally, these soils are less than ten inches in depth, well drained, and have a medium available water holding capacity. Major problems on these soils are erosion and climatic limitations, and recommended land treatment measures are forest or rangeland with good irrigation practices (Wyoming State Engineer's Office, 1972). Steep mountains, with elevations between 6,800 and 14,000 feet, have soils classified as loamyskeletal and mixed and range from 10 - 60 inches in depth. They are well to poorly drained, and have a low to medium water-holding capacity. Major soil problems are cold climate and steep slopes, and the recommended land treatment is continued forestland management (Wyoming State Engineer's Office, 1972). Most of the cropland in the basin is found on fans, rolling hills, and bottomland at elevations of 6,000 to 6,800 feet. Low average annual precipitation at these elevations dictates irrigation for most crops, and a freeze-free season from 0-50 days limits crop production to grass, hay, and some small grain. Soils in this area consist of fine to course loams, and fine to course silts and mixes, and range from 17 - 60 inches in depth. These soils vary from poorly to well drained, with low to high available moisture holding capacities. Major soil problems are water erosion, wetness, and sensitivity to drought. Recommended land treatment measures are residue management, cross-slope operations, cropping sequence, drainage where necessary, and range management (Wyoming State Engineer's Office, 1972).

FLUVIAL GEOMORPHOLOGY

The gradient of the Snake and Gros Ventre rivers through the Jackson Hole area is about 19 and 38 feet per mile, respectively. Some reaches of these streams are considered braided, while multiple channel reaches are the most common, and meandering patterns are limited to reaches with lower gradients and sediment inputs. As a result of the gradients, tributaries draining the mountains tend to have high resultant velocities even during low flows. In flood, they transport large bedloads and spread out through an ever increasing secondary network of side channels, eroding the banks, changing courses frequently, and reforming the channel bed during a single flood event (U.S. Army Corps of Engineers, 1989). The Gros Ventre River is a cobble-bed mountain stream that drains approximately 600 square miles of eastern Jackson Hole and the mountains further east. The river channel is steeply sloped and subject to heavy bedloads originating from rock and cobble deposited by numerous landslides (Love and Reed, 1968). The river is wide and braided in areas where geologic materials are of low erosion resistance, while areas of high resistance result in the river being confined to a single entrenched channel of low sinuosity (Campbell and Lasley, 1990). Limited geomorphic studies (Skinner, 1977; Marston, 1993; and Mills, 1991) have been conducted in the park on a site/issue specific basis, but a comprehensive analysis of the fluvial geomorphic processes characterizing Grand Teton National Park and surrounding regions has not been conducted. General observations by the author include:

. The streams within Grand Teton National Park drain a recently glaciated and tectonically unstable region. Fluvial geomorphic processes are dominated by mountain building forces and the glacial legacy, resulting in streams that are inherently dynamic because they must continually adjust to changing gradients, sediment supplies, and other factors that control stream "stability".

. Stream reaches within Jackson Hole, predominantly contain gravel and cobble bedloads, with sand and silt intermixed or deposited in areas of slower velocities.

. As a result of the tectonic lowering of Jackson Hole and the high sediment supply from the surrounding mountains and glacial deposits, streams within Jackson Hole tend to aggrade. The highest rates of aggradation occur near the mountain fronts and several streams flow on alluvial fans where they exit the mountains.

. The Snake River through Jackson Hole is naturally characterized by varying levels of stability, predominantly resulting from proximity to sediment supplies (i.e., very stable from Jackson Lake to Pacific Creek where the lake traps sediment, to unstable below the tributary confluences and terrace cutbanks where sediment is contributed).

. Instability and aggradation are natural phenomenon dominating the region for eons, and the plant and animal life inhabiting the park have evolved to co-exist, and in some cases be dependant upon, this instability.

. The shallow soils typical of the area's flood plains result in shallow rooted riparian vegetation, which furthers the tendency for high bank erosion and channel dynamics.

The construction of park facilities, such as the headquarters within the Snake River flood plain at Moose, bridges over tributaries, irrigation headgates, streamside campgrounds, and boat accesses, demands a level of stability not naturally present in the region's water courses. Therefore, significant efforts have been made to increase the stability of some stream reaches, requiring large expenditures of capital and manpower and interfering with natural stream and riparian processes. Issues discussed later that effect or arise from fluvial geomorphic processes include road aggregate mining, hydrologic modifications, and flood plain management.

Source National Park Service, Water Resources Division

References

Campbell, T.M., and Lasley, C. L., 1990, Minimum Instream Flows for the Lower Gros Ventre River , Teton County , Wyoming : Lower Gros Ventre River Study Group, Wilson , Wyoming , 52 pp.

Cox, E.R., 1974, Water Resources of Grand Teton National Park: U. S. Geological Survey, Open-file report, 114 pp.

Love J.D., and Reed, J.C. Jr., 1968, Creation of the Teton Landscape, the Geologic Story of Grand Teton National Park : Grand Teton Natural History Association, Moose, Wyoming , 120 pp.

Marston, R. A., 1993, Changes in Geomorphic Processes in the Snake River Following Impoundment of Jackson Lake and Potential Changes due to 1988 Fires in the Watershed: Department of Geography and Recreation, University of Wyoming , Laramie , WY , 129 pp.

Mills, J.D., 1991, Wyoming 's Jackson Lake Dam , Horizonatal Channel Stability, and Floodplain Vegetation Dynamics: Masters thesis, University of Wyoming , Laramie , Wyoming , 54 PP .

Noland, B.T., and Miller, K.A., 1995, Water Resources of Teton County , Wyoming , Exclusive of Yellowstone National Park : U. S. Geological Survey, Water Resources Investigation Report 95-4204, 76 pp.

Skinner, M.M., 1977, Sedimentation Problems on the Buffalo Fork River, Gros Ventre River, Spread Creek, and Pilgrim Creek: Contract Report for Teton County 208 Planning Agency, Civil Engineering Department, Colorado State University, Fort Collins, CO.

U.S. Army Corps of Engineers, 1989, Jackson Hole Wyoming Flood Protection Project, draft O&M Decision Document and EIS: Walla Walla District, Walla Walla , Washington , 148 PP.

Wyoming State Engineer's Office, 1972, Water and Related Land Resources of the Snake River Basin, Wyoming:, Wyoming State Engineer's Office., Wyoming Water Planning Program, Report # 12, Cheyenne,WY, 152 pp.

Journey Through the Past: A Geology Tour
Read the past as you view the Teton Range today. The ancient geologic processes that shaped the mountains and valley have left visible marks. Watch millions of years of dynamic geology unfold before you while exploring Grand Teton National Park.

Two rectangular blocks of the Earth's crust moved like giant trap doors, one swinging skyward to form the mountains, the other hinging downward to create the valley. Wind, rain, ice, and glaciers constantly eroded the rising range. Meanwhile, enormous glaciers and torrential meltwaters flowed southward carrying cobbles, gravel, and coarse sand and periodically re leveled the floor of the sinking valley.

Rock Formation
The geologic story of this range starts with the formation of the rocks that make up the mountains, rocks far older than the mountains themselves. The process began over 2.5 billion years ago when sand and volcanic debris settled in an ancient ocean. For millions of years, additional sediment was deposited and buried within the earth's crust. Heat and pressure metamorphosed (changed) the sediment into gneiss, the rocks that comprise the main mass of the Teton Range. The stress of metamorphosis caused minerals to segregate. Today, alternating light and dark layers identify banded gneiss, readily seen in Death Canyon and other canyons in the Teton Range.

Next, magma (molten rock) forced its way up through cracks and zones of weakness in the gneiss. This igneous (formed by heat) rock slowly cooled, forming light-colored dikes of granite, inches to hundreds of feet thick. Look for larger dikes as you view the mountains from the Jenny Lake and String Lake areas. Uplift and erosion have exposed the granite that now forms the central peaks of the range.

Diabase, a dark-colored igneous rock, 1.3 billion years ago flowed up through the gneiss and granite, resulting in the prominent vertical dikes seen today on the faces of Mt. Moran and the Middle Teton. The diabase dike on Mt. Moran protrudes from the face because the gneiss surrounding it erodes faster than the diabase. The diabase dike on the Middle Teton is recessed because the granite of the central peaks erodes more slowly than the diabase.

Shallow seas that covered the Teton region 600 million to 65 million years ago have left sedimentary formations, still visible at the north and south ends of the Teton Range and also on the west slope of the mountains. Marine life, especially tiny trilobites, corals and brachiopods, flourished in the shallow seas covering this area.

The seas repeatedly advanced and retreated. During retreat of the younger seas, this area became a low-lying coastal plain frequented by dinosaurs. Fossilized bones of a horned dinosaur, the Triceratops, have been found east of the Park near Togwotee Pass.

Mountain Building
Compression of the earth's crust 80 million to 40 million years ago caused uplift of the Rocky Mountain chain, from what is now Mexico to Canada. While the mountains on the south and east formed during this period, the rise of the Teton Range as we now see it had not yet begun.

Stretching and thinning of the earth's crust caused movement along the Teton fault to begin about 6 - 9 million years ago. Every few thousand years, when the elasticity of the crust stretches to its limit, a fault (or break) of about 10 feet occurs, relieving stress in the earth's crust. The blocks on either side of the fault moved, with the west block swinging skyward to form the Teton Range, the youngest and most spectacular range in the Rocky Mountain chain. The east block dropped downward, forming the valley called Jackson Hole. The valley block under your feet has actually dropped down four times more than the mountain block has uplifted.

Total vertical movement along the Teton fault approaches 30,000 feet. Evidence for the amount of movement comes from the present location of the Flathead Sandstone. Activity along the Teton fault separated this formation on the opposing blocks. On the summit of Mt. Moran 6,000 feet above the valley floor, lies a pink cap of Flathead Sandstone, visible when the snow has melted. On the valley side of the fault, this formation lies buried at least 24,000 feet below the surface.

Early nineteenth century fur trappers referred to high mountain valleys as "holes". When they named this valley Jackson Hole, they were geologically correct! Today the sheer east face of the Teton Range, rising abruptly more than a mile above the valley, captures our attention more than the valley does. Rocks and soil, thousands of feet thick, transported into the valley over the past several million years, mask the subsidence of the valley.

Some of the deposits filling Jackson Hole contain innumerable rounded rocks varying in color from white to pink and purple. These quartzite rocks eroded from an ancestral mountain range probably located 20 to 70 miles northwest of the Teton Range. Rivers rounded the quartzite into cobblestones as they carried the rocks into this area.

Volcanism
Vast clouds of volcanic ash blew into the Teton region from the west and north, beginning more than 20 million years ago. White ash accumulated on the sinking floor of Jackson Hole 9 million to 10 million years ago, leaving deposits nearly one mile thick. Between 6 million and 600 thousand years ago, fiery incandescent clouds of gaseous molten rock originated in what is now central Yellowstone Park and flowed southward on both sides of the Teton Range. Remnants of this flow are exposed on Signal Mountain and on the north end of the Teton Range.

Glaciation
The sculpturing influence of ice has provided a final spectacular touch to a scene that already boasted mountains rising sharply from a broad, flat valley. About 150,000 years ago this region experienced a slight cooling that allowed an accumulation of more and more snow each year. Eventually glaciers (masses of ice) began to flow from higher elevations. Over two thousand feet thick in places, the ice sheet flowed from north to south through Jackson Hole. The glacier finally halted south of the town of Jackson and melted about 100,000 years ago. About 60,000 years ago the glaciers returned, first surging from the east down the Buffalo Valley, stopping near the Snake River Overlook. The most recent ice advance flowed from the Yellowstone Plateau south down the Snake River drainage and east from the canyons in the Teton Range, about 20,000 years ago. The Yellowstone ice mass gouged out the depression occupied today by Jackson Lake.

Smaller glaciers flowing eastward down the Teton Range broadened the V-shaped stream canyons into U-shaped canyons, typical evidence of glaciation. Ice flowed from the canyons into Jackson Hole, then melted to form the basins that small lakes occupy today. Glacial lakes include:

Phelps,
Taggart,
Bradley,
Jenny,
String, and
Leigh.

As glaciers flowed down the canyons, rocks and ice smoothed and polished canyon floors and walls. Look for glacial polishing today in Cascade and other canyons. Other telltale signs of glaciation include cirque lakes high up in the canyons, such as Lake Solitude in the north fork of Cascade Canyon. The peaks of the Teton Range became more jagged from frost-wedging, where water freezing in the rocks exerted a prying force, eventually chiseling the rocks free, leaving the sharp ridges and pinnacles seen today.

Although the last great ice masses melted about 15,000 years ago, a dozen re-established glaciers still exist in the Teton Range. Mt. Moran exhibits five glaciers:

Triple Glaciers on the north face,
prominent Skillet Glacier on the east face and
Falling Ice Glacier on the southeast face.

Teton Glacier lies in the shadow of the Grand Teton. One way to view a glacier up close involves a ten-mile hike (twenty miles round trip) up the south fork of Cascade Canyon to Schoolroom Glacier. It demonstrates all the features of a classic glacier.

Moraines (deposits of glacially-carried debris) accumulated at the terminus of each ice surge. Because moraines contain a jumble of unsorted rocks and soil that retains water and minerals, glacial debris today supports dense lodgepole pine forests. To locate moraines, look for large stands of pines on ridges projecting above the valley floor, such as Timbered Island and Burned Ridge. Glacial moraines also surround the lakes at the base of the peaks.

Where glacial meltwater washed away most of the soil, the cobbles and poor, thin soil left behind cannot retain moisture or nutrients. Sagebrush, certain wildflowers and grasses can tolerate such desert-like growing conditions. Thus the geologic history of a region determines the vegetation and ultimately the wildlife, too.

Collecting Rocks
Federal law prohibits collecting in National Parks. Please leave rocks where you find them so that others may enjoy the intact geologic story.

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The General park map handed out at the visitor center is available on the park's map webpage.

For information about topographic maps, geologic maps, and geologic data sets, please see the geologic maps page.

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A geology photo for this park can be found here.

For information on other photo collections featuring National Park geology, please see the Image Sources page.

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Currently, we do not have a listing for a park-specific geoscience book. The park's geology may be described in regional or state geology texts.

Please visit the Geology Books and Media webpage for additional sources such as text books, theme books, CD ROMs, and technical reports.

Parks and Plates: The Geology of Our National Parks, Monuments & Seashores.
Lillie, Robert J., 2005.
W.W. Norton and Company.
ISBN 0-393-92407-6
9" x 10.75", paperback, 550 pages, full color throughout

The spectacular geology in our national parks provides the answers to many questions about the Earth. The answers can be appreciated through plate tectonics, an exciting way to understand the ongoing natural processes that sculpt our landscape. Parks and Plates is a visual and scientific voyage of discovery!

Ordering from your National Park Cooperative Associations' bookstores helps to support programs in the parks. Please visit the bookstore locator for park books and much more.

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For information about permits that are required for conducting geologic research activities in National Parks, see the Permits Information page.

The NPS maintains a searchable data base of research needs that have been identified by parks.

A bibliography of geologic references is being prepared for each park through the Geologic Resources Evaluation Program (GRE). Please see the GRE website for more information and contacts.

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