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-foot (610 m)-high main cone on top of an old basaltic andesite shield volcano. With a volume of 8 to 9 km3, Mount Bailey is slightly smaller than neighboring 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 and 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. Mount Bailey is one of Oregon's Matterhorns.

Diamond Lake is a natural body of water in the southern part of the U.S. state of Oregon. It lies near the junction of Oregon Route 138 and Oregon Route 230 in the Umpqua National Forest in Douglas County. It is located between Mount Bailey to the west and Mount Thielsen to the east; it is just north of Crater Lake National Park.