A tranquil view of Hoover Dam at night. Each year about 10 million people visit Hoover Dam. It's maintained by the U.S. Bureau of Reclamation and became a National Historic Landmark in 1985. View photo »

A time lapse photo from the north-east side of Hoover Dam shows traffic moving across the dam at night. The Federal Highway Administration estimates that each day as many as 17,000 people cross the dam on U.S. Highway 93. View photo »

Water erupts out of the spillways of the Hoover Dam in this photo taken during the 1930's. The seventeen turbine-generators housed inside the dam are capable of producing up to 2,080 megawatts of electricity. This is enough energy to supply Nevada, Arizona and most of California. View photo »

Hoover Dam guide Tom Gailey, gives the dam's 25 millionth visitor, Leroy Zimmerman, a V.I.P. tour of the dam. Zimmerman and his family, on a month-long vacation from Myerstown, Penn., were also given a photo album/scrapbook of the dam and a free lunch. The Hoover Dam hosts about 10 million visitors each year. View photo »

This photo, taken Aug 18, 1981, shows a row of generators lining the inside of the Hoover Dam power plant. At center are the tops of some of the turbines which generate the massive electric power created when water pours down through the turbines. It produces 2,080 megawatts of electrical power, enough to meet the needs of 1 million to 1.5 million people for a year. View photo »

A Grand Canyon tour plane passes just southwest of Hoover Dam. Air tours carry thousands of visitors each year over the dam, the Colorado River and the mountains formed by the river. View photo »

On Oct. 1981 maintenance workers overhauled a stainless steel turbine runner in the A7 generator in the Arizona wing of the Hoover Dam Powerhouse. Turbines from the 17 power generating units produce enough electricity to meet the needs of dozens of cities in California, Nevada and Arizona. View photo »