Imagine visiting Grand Teton National Park 100 million years ago. You would see a much different landscape. Stretching before you would be a great sea depositing layers of sediment on top of 2.5 billion-year-old granite and 2.7 billion-year-old gneiss. Jump forward 30 million years; those seas have retreated, and the collision of tectonic plates begins to up-lift the Rocky Mountains. Another 60 million years pass before a different type of geologic force creates the Teton Range.
The Teton fault extends 40 miles along the base of the Teton Range. About ten million years ago, this region began to stretch and the Earth's crust cracked forming faults. Each time the crust broke; an earthquake up to magnitude 7.5 shook the land tilting the mountains skyward and dropping the valley floor. These sporadic bursts of energy created the abrupt front of the Teton Range as it towers above Jackson Hole. At 13,770 feet, the summit of the Grand Teton rises 7,000 feet above the valley floor. Total vertical displacement across this fault may be up to 30,000 feet. The floor of Jackson Hole may have dropped over 20,000 feet, roughly three times as much as the mountains rose. The jagged skyline, vertical relief and lack of foothills make the Teton Range a sight to behold.
Beginning two million years ago, glaciers repeatedly scoured and sculpted the Teton landscape. Large masses of ice flowed from the topographic high of the Yellowstone Plateau down across the valley of Jackson Hole numerous times leveling the valley floor. At the same time, alpine glaciers flowed down from the high peaks carving U-shaped canyons and gouging out valley lakes. Grand Teton National Park contains many features created during the ice age such as piedmont lakes, U-shaped canyons, knife-like ridges, kettles, and moraines.
Grand Teton National Park today boasts dramatic vistas and a geologic story that is by no means complete. Geologic forces such as erosion and glaciation still sculpt the landscape and a major earthquake will occur in the future. The last major earthquake happened roughly 5,000 years ago, but the fault will lurch into action once again. Imagine a rubber band stretched to its limit; sooner or later it will break. For the Teton fault, it is not a matter of if, but when, it will move again.
Discover Grand Teton allows viewers to explore the geology of the region through a timeline, earthquakes, rocks and forces.
What's shaking in the Intermountain West (Montana, Idaho, Wyoming, Nevada, Utah, Colorado, Arizona and New Mexico)? Visit the "Recent Earthquakes in the Intermountain West" website to learn about recent earthquakes in the area. The site provides local magnitude, times of occurrence and proximity to local towns and cities.
Read the park's geology brochure for more information.