The Hoover Dam is a concrete arch-gravity dam in the Black Canyon of the Colorado River, situated on the border of Nevada and Arizona. Standing 726.4 feet (221.4 m) tall and 1,244 feet (376 m) long, it impounds Lake Mead, the largest reservoir in the United States by volume. Construction of the Hoover Dam between 1931 and 1936 served as a massive public works project of the Great Depression, employing thousands of workers — in fact, when the dam was authorized, nearly 20,000 unemployed individuals flocked to Las Vegas (a city of just 5,000 at the time) in hopes of finding work