Big Horn Mountains

The Bighorn Mountains (Crow: Basawaxaawúua, lit. 'our mountains' or Iisaxpúatahchee Isawaxaawúua, 'bighorn sheep's mountains') are a mountain range in northern Wyoming and southern Montana in the United States, forming a northwest-trending spur from the Rocky Mountains extending approximately 200 mi (320 km) northward on the Great Plains. They are separated from the Absaroka Range, which lie on the main branch of the Rockies to the west, by the Bighorn Basin. Much of the land is contained within the Bighorn National Forest.

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 th

Location: United States.

Mountain range data from Wikidata (CC0). Elevation is the height of the highest peak.