<P> Hoover Dam, originally known as Boulder Dam from 1933 to 1947, when it was officially renamed Hoover Dam by a joint resolution of Congress, 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 . The dam was named after President Herbert Hoover . </P> <P> Since about 1900, the Black Canyon and nearby Boulder Canyon had been investigated for their potential to support a dam that would control floods, provide irrigation water and produce hydroelectric power . In 1928, Congress authorized the project . The winning bid to build the dam was submitted by a consortium called Six Companies, Inc., which began construction on the dam in early 1931 . Such a large concrete structure had never been built before, and some of the techniques were unproven . The torrid summer weather and lack of facilities near the site also presented difficulties . Nevertheless, Six Companies turned over the dam to the federal government on March 1, 1936, more than two years ahead of schedule . </P> <P> Hoover Dam impounds Lake Mead, the largest reservoir in the United States by volume (when it is full). The dam is located near Boulder City, Nevada, a municipality originally constructed for workers on the construction project, about 30 mi (48 km) southeast of Las Vegas, Nevada . The dam's generators provide power for public and private utilities in Nevada, Arizona, and California . Hoover Dam is a major tourist attraction; nearly a million people tour the dam each year . The heavily traveled U.S. Route 93 (US 93) ran along the dam's crest until October 2010, when the Hoover Dam Bypass opened . </P> <P> As the United States developed the Southwest, the Colorado River was seen as a potential source of irrigation water . An initial attempt at diverting the river for irrigation purposes occurred in the late 1890s, when land speculator William Beatty built the Alamo Canal just north of the Mexican border; the canal dipped into Mexico before running to a desolate area Beatty named the Imperial Valley . Though water from the Imperial Canal allowed for the widespread settlement of the valley, the canal proved expensive to maintain . After a catastrophic breach that caused the Colorado River to fill the Salton Sea, the Southern Pacific Railroad spent $3 million in 1906--07 to stabilize the waterway, an amount it hoped vainly would be reimbursed by the Federal Government . Even after the waterway was stabilized, it proved unsatisfactory because of constant disputes with landowners on the Mexican side of the border . </P>

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