WYOMING — According to the Yellowstone Volcano Observatory’s (YVO) latest Caldera Chronicles, not all mountains in the Yellowstone National Park (YNP) region are volcanic in origin. The Wind River Range is one example of an ancient pile of rocks sculpted by more recent tectonic and glacial forces.
Stanley P. Mordensky, research geologist at the Geology, Minerals, Energy and Geophysics Science Center, writes that the Wind River Range extends roughly 136 miles from Dubois to South Pass City, Wyoming, with a width of approximately 40 miles. Gannett Peak (13,810 feet) isn’t just the highest point in the Wind River Range but also in the state of Wyoming.
According to Mordensky, the rocks in these mountains range from 3.4 to 2.3 billion years old.
“In other words, the majority of the rock that now composes the Wind River Range is older than half the age of the Earth and was once deeply buried beneath the Earth’s surface,” Mordensky writes.
During portions of the Paleozoic (542 to 251 million years ago) and Mesozoic (251 to 65.5 million years ago) eras, Mordensky confirms the region was part of an inland sea, as evidenced by deposits of sandstone, mudstone and limestone found along the foothills of the Wind River Range. But Mordensky writes that at some point, those rocks began to experience uplift between what most geologists agree was about 65 million years ago and about 50 million years ago, although some evidence suggests that the uplift may have begun tens of millions of years earlier and lasted tens of millions of years longer.
Evidence of erosion also suggests that the uplift did not occur as a single episode but in pulses.
Mordensky writes that over the duration of the cumulative deformation, uplift raised the rocks of the Wind River by about nine miles vertically and transported the rocks laterally by about 16 miles. The faults that accommodated this displacement, located to the southwest of the Wind River Range, have remained aseismic “in historical times.”
Following the uplift of the Wind River Range, glaciations like the Bull Lake (about 150,000 to 130,000 years ago) and Pinedale (22,000-14,000 years ago) events sculpted the mountains and created the landscape recognized and enjoyed today.
