Hoover Dam was built between 1931-1936 on the border of Nevada and Arizona. It was constructed as a concrete anti-gravity dam across the Black Canyon of the Colorado River. The dam cost over $100 million and hundreds of lives to build. Six Companies, Inc was awarded the contract to build the dam. They established a new city called Boulder City to house the thousands of workers during construction. Hoover Dam provides hydroelectric power and irrigation water to parts of the western United States.