Hoover Dam

In 1928 Congress authorized $175 million for construction of a dam on the Colorado River to control destructive floods, provide a steady water supply to seven Colorado River basin states, and generate electricity. Considered one of the seven wonders of the industrial world, the art deco Hoover Dam is 726 feet high (the equivalent of a 70-story building) and at the base it's 660 feet thick (more than the length of two football fields). Construction required 4.4 million cubic yards of concrete—enough to build a two-lane highway from San Francisco to New York.