Unity Dam, located about 40 miles southwest of Baker, Oregon, is a rolled, zoned earthfill-type structure, 82 feet high above its foundation. The dam contains 254,000 cubic yards of earth and rock. The original total capacity (1938) was reported at 27,000 acre-feet. A 1991 sedimentation survey estimated the total capacity at 25,502 acre-feet (active 24,970 acre-feet).
The reservoir basin is a portion of a large depression lying between the Elkhorn Range on the north, the Blue Mountains to the west and the Ironsides Mountains on the south. Uplift of the surrounding ranges resulted in the deformation of existing formations, chiefly lava, and was accompanied by faulting on a moderate scale.