Lake Berryessa is the largest lake in Napa County, California, a reservoir in the Vaca Mountains created by the construction of Monticello Dam on Putah Creek. Construction of the dam began in 1953, was completed in 1958, and the reservoir filled by 1963 — at the time making it the second-largest reservoir in California after Shasta Lake. The reservoir was named for the Berryessa family; José Jesús and Sexto “Sisto” Berryessa were granted Rancho Las Putas in 1843. The former farming town of Monticello, founded by Ezra Peacock in 1867, was abandoned and flooded to create the lake; its evacuation was documented by photographers Dorothea Lange and Pirkle Jones in Death of a Valley (1960).
The lake supplies water and hydroelectricity to communities including Vacaville, Suisun City, Vallejo, and Fairfield, and to Travis Air Force Base. It is managed as part of the broader Solano Project under the federal Bureau of Reclamation.
In the context of the Zodiac case, Lake Berryessa is significant as the site of the Lake Berryessa attack, in which Pacific Union College students Bryan Calvin Hartnell and Cecelia Ann Shepard were attacked on a small island connected by a sand spit to Twin Oak Ridge on the evening of 1969-09-27. The attack is one of the canonical Zodiac Killer crimes.