Monticello Dam, Largest Drain Hole

Monticello Dam is a dam in Napa County, California, United States constructed between 1953 and 1957. It contains 326,000 cubic yards (249,000 m³) of concrete. The dam impounded Putah Creek to cover the former town of Monticello and flood Berryessa Valley to create Lake Berryessa, the second-largest lake in California. The capacity of the reservoir is 1,602,000 acre·ft (1,976,000 dam³). Water from the reservoir is supplied mostly to the North Bay area of San Francisco. The dam is noted for its classic, uncontrolled spillway with a rate of 48,400 cubic feet per second (1370 m³/s) and a diameter at the lip of 87 ft (27 m). The Monticello Dam Powerplant was built at the dam in 1983 and has three generators. The electrical power is sent mostly to the North Bay area of San Francisco.