Jackson Gulch Dam is a rock-faced earthfill structure 180 feet high with a concrete cutoff wall. The reservoir is off-stream on Jackson Gulch, 5 miles north of Mancos, and has a total capacity of almost 10,000 acre-feet. The dam does not have a spillway. The 280-cubic-foot-per-second-capacity outlet works is a concrete pressure conduit from trashrack to gate chamber, and a steel pipe from gate chamber to two hollow jet valves. The Inlet Canal extends from the West Mancos River to the reservoir.
Below elevation 7790 on the left abutment and 7805 on the right abutment Jackson Gulch Dam will rest on a layer of wash composed of gravel, rock and clay-silt four to eleven feet thick, apparently quite impervious, overlying a sandy shale of varying degrees of hardness, and Dakota sandstone. Above these elevations one test pit near each end of the dam shows two to five feet of soil, compacted clay and a few boulders overlying 28 to 32 feet of gravel and boulders, which in turn rest on shale. Top soil and loam varies from 1 to 2.5 feet in depth. In the valley bottom the silt is stripped above the dam axis to the sandstone.