High Quality Content by WIKIPEDIA articles! The American Falls Dam is a concrete gravity-type dam located near the town of American Falls, Idaho, on river mile 714.7 of the Snake River. The dam and reservoir are a part of the Minidoka Irrigation Project on the Snake River Plain and are used primarily for flood control, irrigation, and recreation. When the original dam was built by the Bureau of Reclamation, the residents of American Falls were forced to relocate three-quarters of their town to make room for the reservoir. A second dam was completed in 1978 and the original structure was demolished. A lava dam created a broad shallow lake in the area of the Raft River during late Pliocene time, over one million years ago. Much of the basin filled with fine sand, silt, and gravel; then the dam was breached and the lake drained. These sediments lie beneath most of the present-day American Falls Reservoir. At other times the Snake River was dammed completely by basalt flows extruded from vents. One lava dam a few miles downstream from the present American Falls Dam formed a reservoir in which more than 80 feet of sediments were deposited.