Hoover Dam (36°0′56″N, 114°44′16″W), also known as Boulder Dam, is a concrete gravity-arch dam in the Black Canyon of the Colorado River, on the border between the states of Arizona and Nevada. The dam, located 30 miles southeast of Las Vegas, is named after Herbert Hoover, who played an instrumental role in its construction, first as Secretary of Commerce and then later as President of the United States. Construction began in 1931 and was completed in 1936, over two years ahead of schedule. The dam is operated by the Bureau of Reclamation of the U.S. Department of the Interior. Listed on the National Register of Historic Places in 1981, Hoover Dam was designated a National Historic Landmark in 1985.