Mason Dam is a water conservation project of the United States Bureau of Reclamation, an earthen and rockfill dam originally constructed from 1965 through 1968.
[1] Owned by the Bureau, it is operated by the local Baker Valley Irrigation District.
The nearby Thief Valley Reservoir from 1932 is part of the same Baker Project.
The dam is 167 feet (51 m) high, and the reservoir has a capacity of 114,000 acre-feet (141,000,000 m3).
It impounds the water of the Powder River to create Phillips Reservoir, which covers 2,235 acres (904 ha) and offers recreational fishing, boating, camping, etc.