Monticello Dam is a dam in Napa County, California, United States constructed between 1953 and 1957. It is a medium concrete-arch dam with a structural height of 304 ft (93 m) and a crest length of 1,023 ft (312 m). 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).