Originally known as Boulder Dam, this concrete arch-gravity dam in the Black Canyon of the Colorado River was the biggest concrete structure of its time. Built during the Great Depression, Hoover Dam took massive efforts to complete with thousands of people working for 5 years (1931-1936). It ultimately claimed over 100 lives. The dam impounds Lake Mead, the largest reservoir in the United States by volume, and produces hydroelectric power. It is 726.4 ft (221.4 m) tall and 1,244 ft (379 m) long.