Bighorn Mountains, a range in north-central Wyoming and southern Montana. They are part of the Rocky Mountains. The range is 120 miles (195 km) long and forms a barrier between the Great Plains on the east and the Bighorn Basin on the west. Bighorn National Forest is in the Wyoming section. The highest peaks, all in Wyoming, include Cloud Peak (13,175 feet [4,016 m]), Mather Peak (12,420 feet [3,786 m]), and Hazelton Peak (10,545 feet [3,214 m]).