The Hoover Dam was constructed on the Colorado River between 1930-1936. It was originally named Boulder Dam and cost $49 million to build. The dam is 660 feet thick, 1,244 feet long and impounds Lake Mead, the largest reservoir in the United States. It provides flood control, water storage and hydroelectric power, helping to reclaim agricultural land in California. At the time of completion, it was the largest concrete structure and public works project in U.S. history.