Hoover Dam is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the U.S. states of Nevada and Arizona. It was constructed between 1931 and 1936 during the Great Depression and was dedicated on September 30, 1935, by President Franklin D. Roosevelt. Its construction was the result of a massive effort involving thousands of workers, and cost over one hundred lives. It was referred to as the Hoover Dam after President Herbert Hoover in bills passed by Congress during its construction; it was named the Boulder Dam by the Roosevelt administration. The Hoover Dam name was restored by Congress in 1947.