Hoover Dam is a concrete dam in the Black Canyon of the Colorado River, on the border between the U.S. states of Arizona and Nevada. When completed in 1936, it was both the world's largest electric-power generating station and the world's largest concrete structure.
This dam, located 30 mi (48 km) southeast of Las Vegas, Nevada, is named after Herbert Hoover, who played an instrumental role in its construction. Construction began in 1931, and was completed in 1936, more than two years ahead of schedule.
Hoover Dam was designated a National Historic Landmark in 1985. Lake Mead is the reservoir created by the dam, named after Elwood Mead, who oversaw the construction of the dam.
For more detail, please refer to http://en.wikipedia.org/wiki/Hoover_Dam