The 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 Nevada and Arizona. The dam impounds Lake Mead, the largest reservoir in the United States by volume. It was constructed between 1931 and 1936 during the Great Depression and was dedicated on September 30, 1935, by President Franklin D. Roosevelt to President Herbert Hoover. Its construction was the result of a massive effort involving thousands of workers, and cost over one hundred lives. Hoover Dam is a major tourist attraction; nearly a million people tour the dam each year. The heavily travelled U.S. 93 ran along the dam's crest until October 2010, when the Hoover Dam Bypass opened.