The main Teton range is categorized as a fault block mountain range and is part of the Teton fault. The fault line is difficult to spot because it is covered in debris from erosion and glaciers. You can see the Teton fault in the steep and straight mountain faces, no foothills, and the lack of symmetry within the Teton mountain range. The rock layers at the top of Mount Moran are the same as those that can be found 24,000 feet under Jackson Hole—a full 30,000 feet of separation.
The Teton fault is classified as a normal fault, which means the crust is pulling apart; some crust goes up and some crust slides down. The Tetons are considered young on a geologic timescale; they are about 9 million years old. The range is made up mostly of gneiss with some granite and dikes of diabase with limestone and sandstone rock on top—besides the sedimentary rock, those hard rocks take a lot of time to weather away. In fact, the Tetons are uplifting faster than they can erode! Over the course of their lifetime, they grew an average of one foot every 350 years, but in the last 150,000 years they grew one foot every 100 years. The Tetons are still getting larger and earthquakes are common even though they are typically small. Even though Jackson Hole and the Tetons seem still and content, they are still under stress and in motion.
Written by Celia Karim
PC: Anne Guzzo