The BigHornMountains 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 miles (320 km) northward on the Great Plains.
The Bighorn Mountains consist of over 9,000 feet 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.
The highest peaks within the BigHorns are located in Wyoming in the 1.1 million acre (4,500 km²) Bighorn National Forest.