Geology of the Grand Teton area
Perhaps 3 billion years ago in Precambrian time, sand, limey ooze, silt and clay were deposited in a marine trough (accurate dating is not possible, due to subsequent partial recrystallization of the resulting rock).
These rocks were 5 to 10 miles (8.0 to 16.1 km) below the surface when orogenies (mountain-building episodes) around 2.8 to 2.7 billion years ago intensely folded and metamorphosed them, creating alternating light and dark banded gneiss and schist.
[6] Early in Cambrian time a shallow seaway, called the Cordilleran trough, extended from southern California northeastward across Nevada into Utah and Idaho.
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.
The Mississippian Madison Limestone is 1,000 feet (300 m) thick and is exposed in spectacular vertical cliffs along canyons in the north, west, and south parts of the Tetons.
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.
[8] 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 dinosaurs (a fossilized Triceratops was found east of the park near Togwotee Pass).
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.
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.
Another warm, shallow sea, the Western Interior Seaway, then partly and sometimes completely covered the Teton region along with most of Wyoming, About 10,000 feet (3,000 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.
Fine-grained volcanic ash from volcanoes west and northwest of the Teton area was periodically deposited in the quiet shallow water of the Western Interior Seaway throughout Cretaceous time.
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.
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.
[9] Some 60 million years ago, these forces uplifted the low-lying coastal plain in the Teton region and created the north–south-trending thrust faults of the nearby Wyoming Overthrust Belt.
[9] Uplift intensified and climaxed a few million years later early in the Eocene epoch when large thrust and reverse faults created small mountain ranges separated by subsiding sedimentary basins.
Gravel, quartzite cobbles, and sand from this erosion eventually became the 5,000-foot (1,500 m) thick Harebell Formation seen today as various conglomerates and sandstones in the northern and northeastern parts of the park.
[13] Blocks of the brittle upper crust responded by breaking along roughly parallel north-to-south trending normal faults 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).
[13] An eastward-moving intensification of this process began 17 million years ago, creating the Basin and Range geologic province in Nevada and western Utah.
[15] Around 10 million years ago,[13] Jackson Hole's first large freshwater lake was impounded by east–west fault movement in what is today the southern end of the park.
[16] The resulting Teewinot Formation of lakebed sediments sits directly on the Colter and consists of limestones and claystones mixed with volcanic material and fossilized clams and snails.
The lake was dry by the time a series of enormous pyroclastic flows from the Yellowstone area buried Jackson Hole under welded tuff.
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 glaciations in the Pleistocene epoch saw the introduction of large glaciers in the Teton and surrounding ranges, which flowed all the way to Jackson Hole during at least three ice ages.
[19] 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.
[19] This continental-sized glacial system stripped all the soil and vegetation from countless valleys and many basins, leaving them a wasteland of bedrock strewn with boulders after the glaciers finally retreated.
Bull Lake helped repair some of the damage of the Buffalo event by forming smaller glaciers which deposited loose material over the bedrock.
Many of these piles of glacial rubble created depressions that in modern times are filled with a series of small lakes (Leigh, String, Jenny, Bradley, Taggart, and Phelps).
[22][23] Stressed by snow melt, the resulting 5 miles (8.0 km) long and 200 feet (61 m) deep lake breached the debris dam on May 18, 1927, and flooded the town of Kelly, Wyoming, killing six.
