Completed in 1967 on land formerly part of Rancho San Luis Gonzaga, the reservoir is a joint use facility, being a part of both the California State Water Project and federal Central Valley Project, which together form a network of reservoirs, dams, pumping stations, and of canals and major conduits to move water across California. The San Luis Reservoir is located in Merced County, and has a visitor center located at the Romero Outlook where visitors can learn more about the dam and reservoir. The surface of the reservoir lies at an elevation of approximately , with the O'Neill Forebay below the dam at above sea level. This elevation difference allows for a hydroelectric plant to be constructed - the Gianelli Hydroelectric Plant. Power from this plant is sent to a Path 15 substation, Los Banos via a short power line. Those 500 kV wires, carrying both the power generated here and elsewhere, leave the area and cross the O'Neill Forebay on several man-made islands.