Hoover Dam, also known as Bouler Dam, is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the U.S. states of Arizona and Nevada. When completed in 1935, it was both the world's largest electric power producing facility and the world's largest concrete structure. It was surpassed in both respects by the Grand Coulee Dam in 1945. It is currently the world's 34th largest hydroelectric generating station.