This is an aerial view of the Hoover Dam of the Boulder Canyon project situated in Black Canyon on the Colorado River, on the border of the states of Nevada and Arizona, in Boulder City, Nev., March 13, 1936. A portion of the Mead Lake is shown behind the 731-foot high concrete structure. Water from the lake flows at the ratio of several thousand gallons per second from outlet valves on the Arizona side, below dam. Intake towers are behind the dam on each side. (AP Photo)