Anderson Ranch Dam is an earth rockfill type dam on the South Fork of the Boise River, in Elmore County, Idaho, United States. Its reservoir is plainly called "Anderson Ranch Reservoir" and has a spillway elevation of 4,196 feet (1,279 m) above sea level. The dam is northeast of Mountain Home and several miles north of US 20. When completed in 1950, Anderson Ranch was the tallest dam of its type in the world. Its primary purpose is to provide irrigation water for agriculture, with a secondary purpose of hydroelectric power. Its generating capacity was increased from 27MW to 40 MW in 1986.