Wickiup Dam, with a total capacity of 200,000 acre-feet (active 200,000 acre-feet), completed in 1949, stores water for the irrigation of lands in the North Unit Irrigation District. The dam is a zoned earthfill structure, 100 feet high, with a crest length of 13,860 feet. The dam and dike contain 1,852,000 cubic yards of material. The East Dike closes a low area on the east side of the reservoir, and has a crest length of 3,420 feet. The spillway is an open rock cut with concrete sill at the north end of the East Dike.
Wickiup Dam and Reservoir are situated in forest covered volcanic mountains, consisting of buttes, craters and intervening sediment covered basins. The intermittent out-pouring of lava flows and explosive volcanic activity has created very complex geologic situations in local areas. The porous lava flows, breccia, ash and deposits of water lain sediment can be linked to a huge absorptive sponge with local perched or depressed water tables, where lakes and springs have been created at various elevations, according to the rate of inflow or outflow of water as it adjusts to local topographic and geologic conditions. The readjustments of the earth's crust during and following volcanic activity undoubtedly created huge cracks, fissures and faults through which the surface water can be lost or move to lower subsurface elevations.