6. Hoover Dam
Image Source: Francois Marier
Although we may not hear all that much about hydroelectric power these days, it was important enough in the past to construct massive dams like Hoover Dam to generate electricity. This massive project was completed back in 1936, making it an incredibly impressive project given the equipment that was available at the time. It is nearly 600 feet thick at its base and 45 feet thick near the top, and its construction resulted in the creation of Lake Mead. It still generates enough electricity to serve 1.3 million people in Arizona, California and Nevada.
