Storage for the project is impounded by this 162-foot-high earthfill structure, which contains 3,738,000 cubic yards of material. Vallecito Dam is on the Pine River, 18 miles northeast of Durango. The reservoir has a total capacity of 129,700 acre-feet. The spillway is a gate-controlled, concrete-lined open channel, 2,300 feet long at the right abutment. The outlet works is a twin section concrete conduit through the right abutment of the dam.
Vallecito Dam is located on a terminal glacial moraine that extends across the valley floor and is up to 200 feet thick. The moraine consists of poorly sorted clay, sand gravel and cobbles with localized pockets of loose sand in the vicinity of the river channel. Red to gray micaceous siltstones, shales and sandstones of the Culer Formation (lower Permian) are exposed at both abutments. A 3-foot thick limestone bed is exposed at the left abutment and dips to the northwest at 16 degrees; bedrock at the right abutment dips 2 to 7 degrees to the northwest. The bedrock is highly fractured and subject to erosion. There does not appear to be any unusual settlement of the dam embankment.