Lably
Skip to content

Bighorn Mountains

Mountain range in Wyoming and Montana, United States

  • 10 min read
  • 6 chapters

Related on Lably

Through Great Plains, Fossil and Erosion

Geology

The Bighorns were uplifted during the Laramide orogeny beginning approximately 70 million years ago. They consist of over 9,000 ft (2,700 m) of sedimentary rock strata laid down before mountain-building began: the predominantly marine and near-shore sedimentary layers range from the Cambrian through the Lower Cretaceous, and are often rich in fossils. There is an unconformity where Silurian strata were exposed to erosion and are missing. The granite bedrock below these sedimentary layers is now exposed along the crest of the Bighorns. The Precambrian formations contain some of the oldest rocks in the world, at 3.25 billion years old. Following the uplift, large volumes of sediments, rich in early Tertiary fossils, were deposited in the adjoining basins. The ice ages of the Pleistocene led to extensive glaciation. Though many cirques, U-shaped valleys and glacial lakes can be found in the mountain range, the only remaining active glacier is the Cloud Peak Glacier, which is on the east slope of Cloud Peak.

Geologist N.H. Darton with the U.S. Geological Survey produced one of the earliest studies of geology in the area, drawn from field research from 1901 to 1905.

Despite extensive prospecting in the Bighorns, no major deposits of precious metals have been found to date. Brief gold rushes of placer deposits occurred at Bald Mountain City and Porcupine Creek, and in Big Goose Canyon. The lack of precious metals helped stave off development and settlement in the mountains, in contrast to the Colorado Rockies.

The Madison limestone aquifer provides a significant source of groundwater for the town of Dayton. Limestone karst formations throughout the range contain many fissures and cracks that have developed into extensive cave systems, including Tongue River Cave, and the caves adjacent to Medicine Mountain. The Natural Trap Cave on the west slope of the Bighorns contains numerous remains of prehistoric mammals.

Sign in to keep reading

5 more chapters are free with a Lably account.

More in Geography