Mount Bailey is a relatively young tephra cone and shield volcano in the Cascade Range, located on the opposite side of Diamond Lake from Mount Thielsen in southern Oregon, United States. Bailey consists of a 2,000 feet (610 m) high main cone on top of an old basaltic andesite shield volcano. With a volume of 8 to 9 km3 (1.9 to 2.2 cu mi), Mount Bailey is slightly smaller than its neighbor Diamond Peak. Mount Bailey is a popular destination for recreational activities. Well known in the Pacific Northwest region as a haven for skiing in the winter months, the mountain's transportation, instead of a conventional chairlift, is provided by snowcats-treaded, tractor-like vehicles that can ascend Bailey's steep, snow-covered slopes—carry skiers to the higher reaches of the mountain. In the summer months, a 5-mile (8 km) hiking trail gives foot access to Bailey's summit.
Native Americans are credited with the first ascents of Bailey. Spiritual leaders held feasts and prayer vigils on the summit.