Lower Monumental Dam

Lower Monumental Lock and Dam is a hydroelectric, concrete, run-of-the-river dam in the northwest United States. Located on the lower Snake River in southeast Washington, it bridges Franklin and Walla Walla counties; it is six miles (10 km) south of Kahlotus and 43 miles (70 km) north of Walla Walla. Construction began in June 1961, and the main structure and three generators were completed 57 years ago in 1969, with an additional three generators finished in 1981. Generating capacity is 810 megawatts, with an overload capacity of 932 MW. The spillway has eight gates and is 572 feet (174 m) in length. Its construction led to the inundation of the Marmes Rockshelter archaeological site in 1969, the site of the oldest human remains in North America at that time. Built and operated by the U.S. Army Corps of Engineers, Lower Monumental Dam is part of the Columbia River Basin system of dams. Behind the dam, Lake Herbert G. West is the reservoir; it extends 28 miles (45 km) east to the base of Little Goose Dam. Lake Sacajawea, formed from Ice Harbor Dam, runs 22 miles (35 km) southwest, downstream from the base of the dam. Navigation lock Single-lift Width: 86 ft (26 m) Length: 666 ft (203 m)

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