The Los Vaqueros Reservoir is located in the northern Diablo Range, within northeastern Contra Costa County, northern California.
It was completed by the Contra Costa Water District (CCWD) in 1998 to improve the quality of drinking water for its 550,000 customers in Central and Eastern Contra Costa County.
The reservoir is accessible via Vasco Road which connects Brentwood and Livermore. An expansion project begun in 2010 raised the height of the dam to increase storage capacity from 100,000 acre-ft to 160,000 acre-ft of water.
At the start of February 2017, the reservoir contained 133,700 acre feet (164,900,000 m3) of water.