Hoover Dam, once known as Boulder Dam, is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between Arizona and Nevada. When completed in 1936, it was both the world's largest electric-power generating station and the world's largest concrete structure. It was surpassed in both these respects by the Grand Coulee Dam in 1945.
Construction began in 1931, and was completed in 1936, more than two years ahead of schedule. Listed on the National Register of Historic Places in 1981, Hoover Dam was designated a National Historic Landmark in 1985.