Rifle Gap Dam is about 5 1/2 miles north of Rifle, at a point where Rifle Creek cuts through the Grand Hogback. The dam is an earthfill structure with a spillway. Rifle Gap Reservoir has a total capacity of 13,602 acre-feet and an active capacity of 12,168 acre-feet, and when full, a surface area of 359 acres.
Rifle Gap Dam is located at the head of a narrow canyon eroded through the Grand Hogback by Rifle Gap. The hogback stands in relief above the adjacent topography because it is formed by Mesaverde sandstone and shale which are most resistant to erosion than formations an either side. Mancos shale outcrops north of the hogbacks and forms a strike valley. The soft Wasatch and Ohio Creek formations are found to the south and form valleys and badlands topography. Prior to construction West Rifle Creek and East Rifle Creek merged to form Rifle Creek at a point approximately 400 feet downstream from the centerline of the dam. Valley fill in the area is as thick as 120 feet or more. The fill consists of coalescing stream deposits, alluvial fan material, and in the upper portions, variable thickness of glacial outwash fan material. A considerable portion of the slopes above the valley are covered with slope wash. A small northwest-southeast fault was mapped between the upper and lower axes during preliminary exploration. The fault is located about 100 feet south of the downstream toe of the dam. Records indicate that rock on either side of the fault is sheared in the left abutment.