Lake Berryessa

Lake Berryessa is the largest lake in Napa County, California. This reservoir in the Vaca Mountains is formed by the Monticello Dam, which provides water and hydroelectricity to the North Bay region of the San Francisco Bay Area.The reservoir was named for the first European settlers in the Berryessa Valley, José Jesús and Sexto "Sisto" Berrelleza (a Basque surname, Anglicized to "Berreyesa", then later respelled "Berryessa"), who were granted Rancho Las Putas in 1843.GeographyThe lake is over 20,000 acres when full. It is approximately 15.5 miles long but only 3 miles wide. It has approximately 165 miles of shoreline.Near the dam on the southeast side of the reservoir is an open bell-mouth spillway, 72ft in diameter, which is known as the Glory Hole. The pipe has a straight drop of 200ft, and the diameter shrinks down to about 28ft. The spillway has a maximum capacity of 48,000 cfs . The spillway operates when there is excess water in the reservoir; in 2017 after heavy rains it started flowing, for the first time since 2006. In 1997 a woman was killed after being pulled inside the spillway.GeologyThe active Green Valley Fault runs parallel to the Lake in the hills to the west.