The Hoover Dam uses its own turbines to power itself

Completed in 1936, the Hoover Dam on the Nevada-Arizona border was the largest concrete structure in the world at the time and required so much electricity to build that a dedicated power plant was constructed first. The dam's 17 turbines generate up to 2,080 megawatts — enough to supply 1.3 million homes. During low-demand periods, electricity is used to pump water back into Lake Mead, storing energy hydraulically. The dam was built two years ahead of schedule and under budget, using a workforce of up to 5,000 men at once in temperatures exceeding 49°C.

Source: Stevens, Hoover Dam: An American Adventure (1988)