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 the U.S. states of Arizona and Nevada. When completed in 1936, it was both the world's largest hydroelectric power generating station and the world's largest concrete structure. The dam weighs in at More than 6,600,000 tons and has more than 45,000 pounds of pressure per square foot at its base. Listed on the National Register of Historic Places in 1981, Hoover Dam was designated a National Historic Landmark in 1985. *Model was created to fit with GE.