Grand Teton Moose, Wyoming 83012 John D
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National Park P.O. Drawer 170 Grand Teton Moose, Wyoming 83012 John D. Rockefeller, Jr., Memorial Parkway 307 739-3300 Journey Through the Past: A Geologic Tour Rock Formation The geologic story of this range starts weakness in the gneiss. This igneous granite of the central peaks erodes more with the formation of the rocks that make (formed by heat) rock slowly cooled, slowly than the diabase. up the mountains, rocks far older than forming light-colored intrusions called the mountains themselves. The process dikes of granite, inches to hundreds of Shallow seas that covered the Teton began over 2.5 billion years ago when feet thick. Look for larger dikes as you region 600 million to 65 million years ago sand and volcanic debris settled in an view the mountains from the Jenny have left sedimentary formations, still ancient ocean. For millions of years, Lake and String Lake areas. Uplift and visible at the north and south ends of the additional sediment was deposited and erosion have exposed the granite that Teton Range and also on the west slope buried within the earth’s crust. Heat and now forms Middle and Grand Teton, of the mountains. Marine life, especially pressure metamorphosed (changed) the the central peaks of the range. tiny trilobites, corals, and brachiopods sediment into gneiss, the rocks that flourished in the shallow seas covering comprise the main mass of the Teton Diabase, a dark-colored igneous rock, this area. Range. The stress of metamorphosis flowed up through the gneiss and granite caused minerals to segregate. Today, 775 million years ago resulting in the The seas repeatedly advanced and alternating light and dark layers identify prominent vertical dikes seen today on retreated. During retreat of the younger banded gneiss, readily seen in Death the faces of Mt. Moran and the Middle seas, this area became a low-lying Canyon (refer to map on back) and Teton. The diabase dike on Mt. Moran coastal plain frequented by dinosaurs. other canyons in the Teton Range. protrudes from the face because the Fossilized bones of a horned dinosaur, gneiss surrounding it erodes faster than the Triceratops, have been found east of Next, magma (molten rock) forced its the diabase. The diabase dike on the the park near Togwotee Pass. way up through cracks and zones of Middle Teton is recessed because the Mountain Building Volcanism Compression of the earth’s crust 80 Teton fault separated this formation on Vast clouds of volcanic ash blew into the million to 40 million years ago caused the opposing blocks. On the summit of Teton region from the west and north, uplift of the Rocky Mountain chain, from Mt. Moran, 6,000 feet above the valley beginning more than 20 million years what is now Mexico to Canada. While floor, lies a pink cap of Flathead Sand- ago. White ash accumulated on the the Snake River Range to the south stone, visible when the snow has sinking floor of Jackson Hole 9 million to and the Gros Ventre Range to the east melted. On the valley side of the fault, 10 million years ago, leaving deposits formed during this period, the rise of the this formation lies buried at least 24,000 nearly one mile thick. Between 2 million Teton Range as we now see it had not feet below the surface. and 600 thousand years ago, fiery yet begun. Early nineteenth century fur trappers incandescent clouds of gaseous molten Stretching and thinning of the earth’s referred to high mountain valleys as rock originated in what is now central crust caused movement along the Teton “holes.” When they named this valley Yellowstone Park and flowed southward fault to begin about 5 – 9 million years Jackson Hole, they were geologically on both sides of the Teton Range. ago. Every few thousand years, when correct! Today the sheer east face of Remnants of this flow are exposed on the elasticity of the crust stretches to its the Teton Range, rising abruptly more Signal Mountain and on the north end limit, a vertical movement of about 10 than a mile above the valley, captures of the Teton Range. feet occurs, relieving stress in the our attention more than the valley does. earth’s crust. The blocks on either side Rocks and soil, thousands of feet thick, of the fault moved, with the west block transported into the valley over the past swinging skyward to form the Teton several million years, mask the subsid- Range, the youngest and most dramatic ence of the valley. Rock Collecting range in the Rocky Mountain chain. The Some of the deposits filling Jackson east block dropped downward, forming Hole contain innumerable rounded rocks Park law prohibits collecting. Please the valley called Jackson Hole. The varying in color from white to pink and leave rocks where you find them so valley block under your feet has actually purple. These quartzite rocks were that others may enjoy the intact geologic dropped down four times more than the carried eastward by large braided story. mountain block has uplifted. streams from what is now central and Total vertical movement along the western Idaho. Rivers rounded the Teton fault approaches 30,000 feet. quartzite into cobblestones as they Evidence for the amount of movement carried the rocks into this area. comes from the present location of Flathead Sandstone. Activity along the rev 2/99 Printed on recycled paper R A N G E N O T Grand Teton Mount Moran E Cascade Canyon T Middle Teton Death Canyon Snake Leigh River String Jenny Lake Range Lake Lake Jackson Lake Bradley Jenny Lake Visitor Center Taggart Lake Lake Phelps Lake TETON VILLAGE COLTER e in BAY Timbered Island ra o M e g id R d e n JACKSON LAKE r u JUNCTION B Signal JACKSON MOOSE Mountain Snake River Overlook N MORAN KELLY Buffalo Valley Gros Ventre Slide Gros Ventre Range Togwotee Pass Glaciation The sculpturing influence of ice has occupy today. Glacial lakes Flathead Sandstone provided a final spectacular touch to a include: Phelps, Taggart, scene that already boasted mountains Bradley, Jenny, String and Diabase Dike rising sharply from a broad, flat valley. Leigh. Skillet Glacier About 150,000 years ago this region experienced a slight cooling that allowed As glaciers flowed down the an accumulation of more and more snow canyons, rocks and ice smoothed each year. Eventually glaciers (masses and polished canyon floors and of ice) began to flow from higher eleva- walls. Look for glacial polishing tions. Over two thousand feet thick in today in Cascade Canyon and places, the ice sheet flowed from north other canyons. Other telltale to south through Jackson Hole. The signs of glaciation include cirque Mount Moran glacier finally halted south of the town of lakes high up in the canyons, such as miles roundtrip) up the south fork of Jackson and melted about 100,000 Lake Solitude in the north fork of Cas- Cascade Canyon to Schoolroom Glacier. years ago. About 60,000 years ago the cade Canyon. The peaks of the Teton It demonstrates all the features of a glaciers returned, first surging from the Range became more jagged from frost- classic glacier. east down the Buffalo Valley, stopping wedging, where water freezing in the near the Snake River Overlook. The rocks exerted a prying force, eventually Moraines (deposits of glacially-carried most recent ice advance flowed from the chiseling the rocks free, leaving the debris) accumulated at the terminus of Yellowstone Plateau south down the sharp ridges and pinnacles seen today. each ice surge. Because moraines Snake River drainage and east from the contain a jumble of unsorted rocks and canyons in the Teton Range, about Although the last great ice masses soil that retains water and minerals, 20,000 years ago. The Yellowstone ice melted about 15,000 years ago, a dozen glacial debris today supports dense mass gouged out the depression re-established glaciers still exist in the conifer forests. To locate moraines, look occupied today by Teton Range. Mt. for large stands of pines on ridges Moran exhibits Jackson Lake. As you enjoy the scenic beauty of projecting above the valley floor, such as five glaciers: Timbered Island and Burned Ridge. Smaller glaciers the Teton Range and Jackson Hole, Triple Glaciers on Glacial moraines also surround the lakes flowing eastward remember that the physical forces the north face, at the base of the peaks. down the Teton that created these features still prominent Skillet Range broadened exert their influence. Mountains Glacier on the Where glacial meltwater washed away east face and the V-shaped continue to rise, while erosion by most of the soil, the cobbles and poor, stream canyons into Falling Ice Glacier thin soil left behind cannot retain mois- U-shaped canyons, wind, water and ice pares the on the southeast ture or nutrients. Sagebrush, certain typical evidence of mountains down. So the story face. Teton wildflowers and grasses can tolerate glaciation. Ice never really ends.... Glacier lies in the such desert-like growing conditions. flowed from the shadow of the Thus the geologic history of a region canyons into Jackson Hole, then melted Grand Teton. One way to view a glacier determines the vegetation and ultimately to form the basins that small lakes up close involves a ten-mile hike (twenty the wildlife, as well..