View source for Geology of the Grand Teton area

The ''' geology of the Grand Teton area''' consists of some of the oldest [[rock (geology)|rock]]s and one of the youngest [[mountain range]]s in [[North America]]. The [[Teton Range]], mostly located in [[Grand Teton National Park]], started to grow some 9 million years ago. An older feature, [[Jackson Hole]], is a [[sedimentary basin|basin]] that sits aside the range.

The  2.5 billion year old [[metamorphic rock]]s that make up the east face of the Tetons are marine in origin and include some [[volcano|volcanic]] deposits. These same rocks are today buried deep inside Jackson Hole. [[Paleozoic]] rocks were deposited in warm shallow [[sea]]s while [[Mesozoic]] deposition transitioned back and forth from marine to non-marine sediments with the [[Cretaceous Seaway]] periodically covering the area late in that era.

[[Image:Teton area perspective map.PNG|thumb|400px|A panoramic perspective map of the Teton area]]

==Precambrian deposition, metamorphism, and intrusion==
Perhaps 3,000 million years ago in [[Precambrian]] time, [[sand]], [[Lime (mineral)|lime]]y ooze, [[silt]] and [[clay]] were deposited in a marine trough (accurate dating is not possible, due to subsequent partial recrystallization of the resulting rock). Interbeded between these layers were [[volcano|volcanic]] deposits, probably from an [[island arc]]. These sediments were later [[lithification|lithified]] into [[sandstone]]s, [[limestone]]s, and various [[shale]]s. These rocks were 5 to 10 miles (8 to 16&nbsp;km) below the surface when [[orogeny|orogenies]] ([[mountain]]-building episodes) around 2,800 to 2,700 million years ago intensely folded and [[metamorphism|metamorphosed]] them, creating alternating light and dark banded [[gneiss]] and [[schist]].<ref>''Geology of U.S. Parklands'', page 592, "Precambrian Rocks", paragraphs 1-2</ref><ref>''Roadside Geology of the Yellowstone Country'', page 5, paragraph 1</ref> Today these rocks dominate the [[Teton Range]] with good examples easily viewable in Death Canyon and other canyons in the Teton Range. The green to black [[Serpentine group|serpentine]] created was used by [[Native Americans in the United States|Native Americans]] to make bowls.

[[Image:Mount Moran diagram.PNG|thumb|300px|The prominent black diabase [[dike (geology)|dike]] on [[Mount Moran]] is representative of similar dikes formed about 1.3 billion years ago.]]
Sometime around 2,500 million years ago, blobs of [[magma]] intruded into the older rock, forming [[pluton]]s of [[granite|granitic]] rock.<ref name="U.S. Parklands page 592">''Geology of U.S. Parklands'', page 592, "Precambrian Rocks", paragraph 2</ref> Extensive exposures of this rock are found in the central part of the range. About 1,300 to 1,400 million years ago in Late Precambrian, 5 to 200 foot (1.5 to 60 m) thick black [[diabase]] dikes intruded as well, forming the prominent vertical dikes seen today on the faces of Mount Moran and Middle Teton (the dike on Mount Moran is {{convert|150|ft|m}}).<ref name="U.S. Parklands page 592"/><ref>''Geology of National Parks'', page 566, section 3</ref> Some of the large dikes can be seen from the Jenny Lake and String Lake areas.

More than 700 million years elapsed between intrusion of the black dikes and deposition of the first Paleozoic [[sedimentary rock]]s.<ref name="CTLcore">{{cite book|last=Love|first=J.D.|title=Creation of the Teton Landscape: The Geologic Story of Grand Teton National Park|work=Precambrian Rocks — The Core of the Tetons |url=http://www.nps.gov/history/history/online_books/grte/grte_geology/sec5.htm|year=1971|publisher=Grand Teton Natural History Association|accessdate=2007-07-02|location=Moose, Wyoming}}</ref>  The Precambrian rocks were uplifted during this gap in the geologic record known as an [[unconformity]]; exposed to [[erosion]] they were 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 subsided 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.<ref name="CTLcore"/>

==Paleozoic deposition==
Deposition resumed in the [[Cambrian]] period and continued through the [[Paleozoic]] era, creating nine major [[formation (geology)|formation]]s which together are 4,000 feet (1,200 m) thick (the only [[geologic period]] in the Paleozoic not represented is the [[Silurian]]). This unit was laid down in a shallow [[sea]] and later became a discontinuous mix of [[dolomite]], limestone, sandstones, and shales. The layers of this unit are relatively undeformed for their age even though periodic upwarp exposed them to [[erosion]], creating  uncomformities . Fossilized [[brachiopod]]s, [[bryozoan]]s, [[coral]]s, and [[trilobite]]s are found in the [[carbonate rock]] layers with the best examples found outside the park in the Alaska Basin. The most complete examples of this unit are found to the west, north, and south of park borders.<ref>For the whole paragraph: ''Geology of National Parks'', page 566, section 4</ref>

===On the edge of a shallow seaway===
[[Image:Teton region in the Lower Cambrian.jpg|thumb|300px|In the Lower (early) [[Cambrian]], the Teton region was on the edge of a shallow seaway called the [[Cordilleran trough]].]]
Early in [[Cambrian]] time a shallow seaway, called the [[Cordilleran trough]], extended from southern [[California]] northeastward across [[Nevada]] into [[Utah]] and [[Idaho]].<ref name="CTLpaleo">{{cite book|last=Love|first=J.D.|title=Creation of the Teton Landscape: The Geologic Story of Grand Teton National Park|work=The Paleozoic Era|url=http://www.nps.gov/history/history/online_books/grte/grte_geology/sec6.htm|year=1971|publisher=Grand Teton Natural History Association|accessdate=2007-07-02|location=Moose, Wyoming}}</ref> The vast gently rolling plain on Precambrian rocks to the east was drained by sluggish westward-flowing [[river]]s that carried sand and mud into the sea. The site of the Teton Range was part of this plain. Slow subsidence of the land caused the sea to spread gradually eastward during Middle Cambrian time flooding the Precambrian plain. 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 the 175 to 200 feet (53 to 60 m) thick [[Flathead Sandstone]].<ref name="CTLpaleo"/> The partly marine Flathead Sandstone is reddish-brown, very hard, brittle and exposures can be found on the north and west flanks of the [[Teton Range]] and [[Gros Ventre Range]].

Mud was laid down on top of the Flathead Sandstone as the shoreline advanced eastward across the Teton area. The resulting soft greenish-gray [[shale]] with beds of purple and green sandstone near its base, became the 100 feet (30 m) thick Wolsey Shale Member of the [[Gros Ventre Formation]].<ref name="CTLpaleo"/> Some shale shows patterns of cracks that formed when the accumulating mud was briefly exposed to the air along [[tidal flat]]s. Small phosphatic-shelled animals called [[brachiopod]]s inhabited these tidal flats but as far as is known, nothing lived on land. Many shale beds are marked with faint trails and borings of worm-like creatures, and a few contain the remains of tiny [[trilobite]]s.

===Covered by a shallow sea===
[[Image:Teton region in the Late Cambrian.jpg|thumb|left|300px|The region was covered by the shallow seaway by the end of the Late Cambrian.]]
As the shoreline continued to move eastward, the 285-foot-thick (87 m) Death Canyon Limestone Member of the Gros Ventre Formation was laid down in clear water farther from shore. It consists of two thick beds of dark blue-gray limestone that are separated by 15 to 20 feet (4.5 to 6 m) of shale.<ref name="CTLpaleo"/> The Death Canyon contains abundant fossil of brachiopods and trilobites in some places. Following this the sea retreated to the west for a short time. The 220-foot-thick (67 m) Park Shale Member of the Gros Ventre Formation was deposited in the shallow muddy water resulting from this retreat. It is a gray-green shale that contains beds of platy limestone [[Conglomerate (geology)|conglomerate]] along with fossils of trilobites and brachiopods.<ref name="CTLpaleo"/> Underwater expanses of [[algae]] flourished in places on the sea bottom and built extensive [[reef]]s. Periodically 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 called 'edgewise' conglomerate.<ref name="CTLpaleo"/> These are widespread in the shale and in overlying and underlying limestone layers.

By Late Cambrian, the shoreline had once again crept eastward, resulting in clearer water that was probably 100 to 200 feet (30 to 60 m) deep. The 100-foot-thick (30 m) [[Gallatin Limestone]] was formed. It consists of blue-gray limestone that is mottled with irregular rusty or yellow patches.<ref name="CTLpaleo"/>  Interrupting the limestone are a few beds of 'edgewise' conglomerate that are indicative of sporadic storms. Now at its maximum extent, the sea covered all of [[Idaho]], [[Montana]], most of [[Wyoming]] and extended eastward across the [[Dakotas]] to connect with shallow seas that covered the eastern [[United States]]. Soon after, a slow uplift caused the sea to gradually retreat westward. The site of the Teton Range emerged above [[sea level]], where, as far as is known, it may have been exposed to erosion for nearly 70 million years.<ref name="CTLpaleo"/>

===Uplift puts the area back on the sea's edge===
[[Image:Teton region in the Early Ordovician.jpg|thumb|300px|Regional uplift had brought the Teton area above sea level by the early [[Ordovician]].]]
The Bighorn Dolomite of Ordovician age forms ragged hard massive light-gray to white cliffs 100 to {{convert|200|ft|m}} high. 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 Group|Madison Limestone]] of Mississippian age is {{convert|1000|ft|m}} 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. The fossils and the relatively pure blue-gray limestone in which they are embedded indicate deposition in warm tranquil seas. The Fossil Mountain Ice Cave—Wind Cave system on the west side of the Teton range was dissolved out of this rock by 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 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 by-products. These elements and compounds are not everywhere concentrated enough to be of economic interest, but their dollar-value is, in a regional sense, comparaible to that of some of the world's greatest mineral deposits.

==Mesozoic deposition==
[[Image:Cretaceous seaway.png|thumb|Cretaceous Seaway]]
[[Mesozoic]] deposition changed from primarily marine to a mix of marine, transitional, and [[continent]]al that varied over time as crustal conditions altered the region. By the close of this era, 10,000 to 15,000 feet (3,000 to 4,500 m) of sediment accumulated in 15 recognized [[formation (geology)|formation]]s. The most extensive non-marine formations were deposited in the [[Cretaceous]] period when the eastern part of the [[Cretaceous Seaway]] (a warm shallow [[sea]] that periodically divided [[North America]] in that period) covered the region. Their sediment came from [[rock (geology)|rock]] eroded from a [[mountain]] chain east of the seaway interbeded with [[Volcanic ash|ash]] from [[volcano]]s west of the seaway in the [[Sierran Arc]] (a long volcanic island chain like the modern [[Andes Mountains]] but in island form). This ash eventually became [[bentonite]], a [[clay]] which expands in [[water]] and thus causes [[landslide]]s in the park.<ref>For the whole paragraph: ''Geology of National Parks'', page 566-567, section 5</ref>

Regional uplift in latest Cretaceous time caused the seaway to retreat and transformed the Grand Teton area into a low-lying coastal plain that was frequented by [[dinosaur]]s (a fossilized ''[[Triceratops]]'' was found east of the park near Togwotee Pass).  [[Coal]]beds were eventually created from the [[swamp]]s and [[bog]]s left behind after the last stand of the seaway retreated. Coal outcrops can be found near abandoned [[mining|mine]]s in and outside of the eastern margin of the park. Outcrops of older Mesozoic-aged formations can be found north, east, and south of the park.

===Sundance Sea covers older deposits===
Most of the basal part of the Mesozoic sequence consists of the more than {{convert|1000|ft|m}} thick, soft, bright-red, and Triassic-aged rocks known as the [[Chugwater Formation]]. The distribution of Mud cracks, fossilized reptiles and amphibians suggest deposition in a [[tidal flat]] environment with a sea several kilometers southwest of Jackson Hole. Evaporite deposits of a few beds of white [[gypsum]] ([[calcium sulfate]]) were likely formed after shallow bodies of salt water were cut off from the sea. A small amount of [[iron oxide]] creates the red color and the formation erodes into colorful hills east and south of the park.

As the Triassic gave way to the Jurassic, wind spread salmon-red colored sand across the red beds of the Chugwater Formation to form the [[Nugget Sandstone]]. The Nugget in turn was buried by the deposits of thin red [[shale]] and thick gypsum of the [[Gypsum Springs Formation]]. Later, a warm, muddy, shallow sea with abundant marine mollusks called the [[Sundance Sea]] started to spread from [[Alaska]] south to [[Wyoming]]. More than {{convert|500|ft|m}} of soft gray fossil-rich [[shale]] and thin beds of [[limestone]] and [[sandstone]]s were deposited. After the sea withdrew, the Jurassic and Lower Cretaceous-aged [[Morrison Formation|Morrison]] and [[Cloverly Formation]]s were laid down on low-lying tropically humid [[flood plain]]s. These formations erode into colorful [[badland]]s of red, pink, purple, and green claystones and mudstones, and yellow to buff sandstones. Large and small [[dinosaur]]s roamed the abundant vegetation and [[swamp]]s.

===Western Interior Seaway expands and retracts===
Brightly colored rocks continued to be deposited as the final period of the Mesozoic, the [[Cretaceous]] dawned. Another warm, shallow sea, the [[Western Interior Seaway]], then partly and sometimes completely covered the Teton region along with most of Wyoming, About {{convert|10000|ft|m}} of drab-colored sand, silt, and clay with some coal beds, volcanic ash layers, and minor amounts of gravel were deposited.

The Western Interior Seaway retreated eastward from the Teton region around 85 million years ago, marked by deposition of the [[Bacon Ridge Sandstone]]. Extensive [[coal swamp]]s formed along and followed the retreating seashore, leaving coal beds 5 to {{convert|10|ft|m}} thick in the Upper Cretaceous strata. Examples of these coal beds are visible in abandoned mines found in the eastern margin of the park. A modern analog of this [[Sedimentary depositional environment|depositional environment]] is the hot and humid climate of the [[Florida Everglades]]. About {{convert|5|ft|m}} of compacted plant material is needed to form {{convert|1|in|mm|sing=on}} of coal.

Fine-grained [[volcanic ash]] from [[volcano]]es west and northwest of the Teton area was periodically deposited in the quiet shallow water of the Western Interior Seaway throughout Cretaceous time. Ash deposited in this manner was later altered to [[bentonite]]; a type of clay used in the foundry industry and as a component of [[oil well]] drilling mud. [[Elk]] and deer in Jackson Hole use exposures of bentonite as a (bitter) [[salt lick]]. Bentonite swells when wet, which causes landslides that sometimes block access roads into Jackson Hole.

Cretaceous-aged rocks in the Teton region form part of a huge east-thinning wedge of crust that is locally almost {{convert|2|mi|km}} thick. Most of these rocks are from debris eroded from slowly rising mountains in the west. Bentonite, [[crude oil]] and [[natural gas]] are commonly produced from the various Cretaceous formations. Enormous coal reserves, with some beds reaching 50 to {{convert|100|ft|m}} thick, are a potentially vast resource.

By the end of the Cretaceous, slightly more than 80 million years ago, the region's landscape was flat and monotonous; a condition that persisted during most of the Late Cretaceous.

===Rocky Mountains rise===
The period of uplift that resulted in the formation of the ancestral [[Rocky Mountains]] is called the [[Laramide orogeny]]. Mountains already existed west and southwest of Wyoming, with progressively older mountains (up to Jurassic age) trending west into Nevada. Latest Cretaceous time saw the formation of a low broad northwest-trending arch along the approximate area of the present Teton Range and Gros Ventre Mountains.

Part of the evidence for the first Laramide mountain building west of the Teton region is the several hundred cubic miles of [[quartzite]] boulders derived from the [[Targhee uplift]], which was located north and west of the northern end of the present-day Teton Range. Streams carried boulders, sand, and clay from the uplift eastward and southeastward across what would become Jackson Hole. Flakes of [[gold]] and some [[mercury (element)|mercury]] are in the resulting [[Harebell Formation]]. Two huge depositional troughs were formed in central and southern Wyoming from fine-grained debris carried farther east and southeast. Many of the larger boulders were derived from Precambrian and possibly lower Paleozoic quartzites, meaning that at least {{convert|15000|ft|m}} of Paleozoic and Mesozoic rock must have been stripped from the Targhee uplift before the quartzites were exposed to erosion.

==Tertiary uplift and deposition==
The [[plate tectonics|tectonic setting]] of western North America changed drastically as the [[Farallon Plate]] under the [[Pacific Ocean]] to the west was shallowly [[subduction|subducted]] below [[North American Plate]]. Called the [[Laramide orogeny]], the compressive forces generated from this collision erased the Cretaceous Seaway, fused the Sierran Arc to the rest of North America and created the [[Rocky Mountains]]. This mountain-building event started in the Mesozoic 80 million years ago and lasted well into the first half of the [[Cenozoic]] era 30 million years ago.<ref name="Windows101">Smith, ''Windows into the Earth'' (2000), page 101</ref>

[[Image:Teton fault block.jpg|thumb|300px|Teton fault block]]
Some 60 million years ago, these forces uplifted the low-lying coastal plain in the Teton region and created the north-south-trending [[thrust fault]]s of the nearby [[Wyoming Overthrust Belt]].<ref name="Windows101"/> Uplift intensified and climaxed a few million years later early in the [[Eocene]] epoch when large thrust and reverse [[Geologic fault|faults]] created small [[mountain range]]s separated by subsiding sedimentary basins. One of the reverse faults, the north-south trending 10 mile (16&nbsp;km) long Buck Mountain Fault, elevated what is today the central part of the [[Teton Range]].

By about 34 million years ago, these forces had uplifted a broad part of western [[Wyoming]] into a continuous high [[plateau]].<ref name="Windows102">Smith, ''Windows into the Earth'' (2000), page 102</ref> This region includes areas now occupied by the Teton Range, [[Gros Ventre Range]], [[Wind River Mountains]] and other mountain ranges to the south and east of the Tetons. A separate area of uplift called the [[Targhee Uplift]] formed north of park borders around this time.

Subsequent [[erosion]] of the Targhee Uplift was driven by steepened [[stream gradient]]s. [[Gravel]], [[quartzite]] cobbles, and [[sand]] from this erosion eventually became the 5,000 foot (1,500 m) thick Harebell Formation seen today as various [[conglomerate (geology)|conglomerates]] and [[sandstone]]s in the northern and northeastern parts of the park.<ref>''Geology of National Parks'', page 568, section 6</ref> In the [[Paleocene]] epoch large amounts of clastic sediment derived from uplifted areas covered the Harebell Formation to become the Pinyon Conglomerate. The lower members of this formation consist of [[coal]] beds and [[claystone]] with [[conglomerate (geology)|conglomerate]] made of quartzite from the Targhee uplift above.<ref>''Geology of National Parks'', page 568, section 7</ref>

The subducting Farallon Plate was eventually completely consumed below the North American Plate, bringing an end to the Laramide orogeny. Hot and semi-plastic rock deep below western North America responded to the lack of compression beginning 30 million years ago by slowly rising; gradually pushing the overlying rock sideways both east and west.<ref name="Windows103">Smith, ''Windows into the Earth'' (2000), page 103</ref> Blocks of the brittle upper crust responded by breaking along roughly parallel north-to-south trending [[normal fault]]s that each have a subsiding basin on one side and a mountain range on the other. This stretching may have begun to tear apart the previously-mentioned high plateau in western Wyoming around this time, but evidence from ancient sediments indicates that the Teton Fault system developed much later (see below).<ref name="Windows103"/>  An eastward-moving intensification of this process began 17 million years ago, creating the [[Basin and Range]] geologic province in [[Nevada]] and western [[Utah]].<ref name="Windows103"/>  Stretching of the crust in this region eventually exceeded 200 miles (320&nbsp;km), doubling the distance between [[Reno, Nevada]] and [[Salt Lake City, Utah]].<ref name="Windows103"/>

Waning of the Laramide orogeny coincided with [[volcanic eruption]]s from two parallel volcanic chains separated by a long valley in the [[Yellowstone]]-[[Absaroka (region)|Absaroka]] area to the north. Huge volumes of volcanic material such as [[tuff]] and ash accumulated to great depth in the Grand Teton area, forming the Absaroka Volcanic Supergroup. Additional eruptions east of Jackson Hole deposited their own debris in the [[Oligocene]] and [[Miocene]] epochs.

[[Image:The Cathedral Group in the Teton Range-NPS.jpg|right|thumb|The northern portion of the [[Cathedral Group]] of high peaks, with [[Teewinot Mountain]] on the left, [[Grand Teton]] center and [[Mount Owen (Wyoming)|Mount Owen]] at right.]]
Sediment collected in various lakes in the area from around 17 to 15 million years ago, becoming the [[Miocene]]-aged [[Colter Formation]].<ref name="Windows103"/> Beginning around 13 million years ago (also in the Miocene), a 40-mile (64-km) long steeply east dipping normal fault system called the [[Teton Fault]] started to vertically move two adjacent blocks.<ref name="U.S. Parklands page 594">''Geology of U.S. Parklands'', page 594, paragraph 3</ref> One block, the Jackson Hole basin, moved down while the other block, containing the westward-tilting eastern part of the Teton Range, moved up; thus creating the youngest mountain range in the [[Rocky Mountains]].<ref name="U.S. Parklands page 594"/> Most of the downward movement occurred right next to the fault, resuling in a 15° tilt of the Colter Formation.<ref name="Windows103"/> No sediment was deposited on top of the tilted Colter Formation for up to three million years, resulting in an [[angular unconformity]] as the tilted Colter partially eroded away.<ref name="Windows104">Smith, ''Windows into the Earth'' (2000), page 104</ref>

Around 10 million years ago,<ref name="Windows103"/> Jackson Hole's first large freshwater [[lake]] was impounded by east-west fault movement in what is today the southern end of the park. Geologists call this [[fault-scarp]] dammed body of shallow water Lake Teewinot and it persisted for around 5 million years.<ref>''Geology of National Parks'', page 568, section 9</ref> The resulting [[Teewinot Formation]] of lakebed sediments sits directly on the Colter and consists of [[limestone]]s and [[claystone]]s mixed with volcanic material and fossilized [[clam]]s and [[snail]]s. All told, sediments in the [[Tertiary]] period attained an aggregate thickness of around 6 miles (10&nbsp;km), forming the most complete non-marine Tertiary geologic column in the [[United States]].<ref>''Geology of National Parks'', page 559, "Cenozoic Rocks...", paragraph 1</ref> Most of these units within the park are, however, buried under younger deposits.

Eventually all the Mesozoic rock from the Teton Range was stripped away and the same formations in Jackson Hole were deeply buried. A prominent outcrop of the pink-colored Flathead Sandstone exits 6,000 feet (1,830 m) above the valley floor on the summit of Mount Moran. Drilling in Jackson Hole found the same formation 24,000 feet (7,300 m) below the valley's surface, indicating that the two blocks have been displaced 30,000 feet (9,100 m) from each other. Thus an average of one foot of movement occurred every 300 years (1&nbsp;cm per year on average).<ref>''Geology of National Parks'', page 562, paragraph 1</ref>

==Quaternary volcanic deposits and ice ages==
Massive [[volcanic eruption]]s from the [[Yellowstone Volcano]] northwest of the area occurred 2.2 million, 1.3 million, and 630,000 years ago. Each catastrophic [[caldera]]-forming eruption was preceded by a long period of more conventional eruptions along even earlier volcanic episodes. One such event sent large amounts of [[Rhyolitic]] lava into the northern extent of Teewinot Lake. The resulting [[obsidian]] (volcanic [[glass]]) has been [[potassium-argon dating|potassium-argon dated]] to 9 million years and was used by [[Native Americans in the United States|Native Americans]] starting thousands of years ago to make [[arrowhead]]s, [[knife|knives]], and [[spear]] points. The lake was dry by the time a series of enormous [[pyroclastic flow]]s from the Yellowstone area buried Jackson Hole under welded [[tuff]]. Older exposures of this tuff are exposed in the Bivouac Formation at [[Signal Mountain (Wyoming)|Signal Mountain]] and Pleistocene-aged tuffs are found capping East and West Gros Venture Buttes (both the mountain and [[butte]]s are small [[fault-block mountain|fault blocks]]).

[[Climate|Climatic]] conditions in the area gradually changed through the Cenozoic as plate tectonics moved North America northwest from a [[sub-tropical]] to a  [[temperate zone]] by the Pliocene epoch. The onset of a series of [[glaciation]]s in the [[Pleistocene]] epoch saw the introduction of large [[glacier]]s in the Teton and surrounding ranges, which flowed all the way to Jackson Hole during at least three [[ice age]]s. [[Cascade Canyon|Cascade]], [[Garnet Canyon|Garnet]], [[Death Canyon|Death]] and [[Granite Canyon]]s were all carved by successive periods of glaciation.

The first and most severe of the known glacial advances in the area was caused by the [[Buffalo glaciation]]. In that event the individual alpine (mountain valley) [[glacier]]s from the Tetons' east side coalesced to form a 2,000 foot (610 m) thick apron of ice that overrode and abraded Signal Mountain and the other three buttes at the south end of Jackson Hole.<ref name="geo 569">''Geology of National Parks'', page 569, section 12, paragraph 2</ref> Similar dramas were repeated on other ranges in the region, eventually forming part of the Canadian Ice Sheet, which at its maximum, extended into eastern [[Idaho]].<ref name="geo 569"/> This continental-sized glacial system stripped all the [[soil]] and [[vegetation]] from countless  [[valley]]s and many basins, leaving them a wasteland of bedrock strewn with boulders after the glaciers finally retreated. Parts of Jackson Hole that were not touched by the following milder glaciations still cannot support anything but the hardiest [[plant]]s (smaller glaciers deposit [[glacial till]] and small rocks relatively near their source, while continental glaciers transport all but the largest fragments far away).

A less severe glaciation, known as [[Bull Lake glaciation|Bull Lake]], started sometime between 160 and 130 thousand years ago. Bull Lake helped repair some of the damage of the Buffalo event by forming smaller glaciers which deposited loose material over the bedrock. In that event, the large glacier which ran down Jackson Hole only extended just south of where [[Jackson, Wyoming]] now sits and melted about 100,000 years ago. 
[[Image:Schoolroom Glacier.jpg|right|thumb|270px|[[Schoolroom Glacier]] is a small remnant glacier left behind from the last major glaciation]]
Then from 25,000 to 10,000 years ago the lower volume [[Wisconsin glaciation]] carved many of the glacial features seen today. Burned Ridge is made of the terminal [[moraine]] (rubble dump) of the largest of these glaciers to affect the area. Today this hummocky feature is covered with [[tree]]s and other vegetation. Smaller moraines from a less severe part of the Pinedale were formed just below the base of each large valley in the Teton Range by alpine glaciers. Many of these piles of glacial rubble created depressions that in modern times are filled with a series of small lakes ([[Leigh Lake|Leigh]], [[String Lake|String]], [[Jenny Lake|Jenny]], [[Bradley Lake|Bradley]], [[Taggart Lake|Taggart]], and [[Phelps Lake (Wyoming)|Phelps]]). [[Jackson Lake]] is the largest of these and was impounded by a recessional moraine left by the last major glacier in Jackson Hole. A collection of [[Kettle (geology)|kettles]] (depressions left by melted stagnant ice blocks from a retreating glacier) south of the lake is called the Potholes. The basins that hold [[Two Ocean Lake]] and [[Emma Matilda Lake]] were created during the Bull Lake glaciation.<ref>For the whole paragraph: ''Geology of National Parks'', page 569, section 12, paragraph 4</ref> Since then [[human]]s have built a [[dam]] over Jackson Lake's outlet to increase its size for [[recreation]]al purposes.

All Pinedale glaciers probably melted away soon after the start of the [[Holocene glacial retreat|Holocene]] epoch. The dozen small [[cirque (landform)|cirque]] glaciers seen today were formed during a subsequent [[neoglaciation]] 5000 years ago.<ref>''Geology of U.S. Parklands'', page 596, paragraph 6</ref> Mount Moran has five such glaciers with [[Triple Glaciers]] on the north face, [[Skillet Glacier]] on the east face, and [[Falling Ice Glacier]] on the southeast face. All the glacial action has made the peaks of the Teton Range jagged from [[frost wedging]]. Other glaciers include [[Teton Glacier]], below the east face of Grand Teton, [[Middle Teton Glacier]], situated on the northeast slopes of Middle Teton, and the fast retreating [[Schoolroom Glacier]], west of Grand Teton at Hurricane Pass.

[[Mass wasting]] events such as the 1925 [[Gros Ventre landslide]] continue to change the area. On June 22, 1925 an earthquake with an estimated magnitude of 4<ref name="Windows106">Smith, ''Windows into the Earth'' (2000), page 106</ref> weakened the side of a mountain located three miles (4.8&nbsp;km) outside of the current park's southeastern border. The next day, 50 million cubic yards (38 million cubic meters) of water-saturated [[Pennsylvanian (geology)|Pennsylvanian]]-aged Tensleep Sandstone slid 1.5 miles (2.4&nbsp;km) from its source on Sheep Mountain and into the [[Gros Ventre River]] valley 2,100 feet (640 m) below, damming the river.<ref name="Windows106"/><ref name=GeolNatParks566>Harris, ''Geology of National Parks'', page 566</ref> Stressed by [[snow]] melt, the resulting 5 mile (8&nbsp;km) long and 200 feet (60 m) deep lake breached the [[debris dam]] on May 18, 1927 and [[flood]]ed the town of [[Kelly, Wyoming]], killing six.<ref name=GeolNatParks566/>

==Notes==
{{Reflist|colwidth=35em}}

==References==
*''Geology of National Parks: Fifth Edition'', Ann G. Harris, Esther Tuttle, Sherwood D., Tuttle (Iowa, Kendall/Hunt Publishing; 1997) ISBN 0-7872-5353-7
*''Geology of U.S. Parklands: Fifth Edition'', Eugene P. Kiver, David V. Harris (New York; John Wiley & Sons; 1999; pages 592-596) ISBN 0-471-33218-6
*''Roadside Geology of the Yellowstone Country'', William J. Fritz, (Mountain Press Publishing Company, Missoula; 1985) ISBN 0-87842-170-X
*National Park Service: Grand Teton National Park [http://www.nps.gov/grte/nat/rock.htm] [http://www.nps.gov/grte/nat/moun.htm] [http://www.nps.gov/grte/nat/glac.htm]
* ''Creation of the Teton Landscape'', 	J.D. Love and John C. Reed, Jr (Grand Teton Natural History Association; Revised Edition edition; 1976) ISBN  9780931895579
* ''Creation of the Teton Landscape: 2nd Revised & Enlarged Edition'', David D. Love, John C. Reed and Kenneth L. Pierce (Grand Teton Natural Hist Association; May 1995) ISBN 978-0931895081

{{DEFAULTSORT:Geology Of The Grand Teton Area}}
[[Category:Geology of Wyoming]]
[[Category:Geology of the Rocky Mountains]]
[[Category:Grand Teton National Park]]