O'Neill Forebay, forebay to the San Luis Reservoir west of Los Banos, California
O'Neill Forebay is a small water reservoir in California's Central Valley that serves as an intermediate storage point for the San Luis Complex. It receives water from the California Aqueduct and the Delta-Mendota Canal, then supplies the William R. Gianelli Pumping-Generating Plant, which pumps the water roughly 300 feet (91 meters) uphill into the larger San Luis Reservoir.
O'Neill Forebay was developed as part of the San Luis Complex, a water management system built in the latter half of the 20th century to modernize California's water distribution. The facility was designed to serve both irrigation and hydroelectric power generation needs across the state.
The site is functionally organized with visible water control gates and channels that visitors can observe from designated areas. The terrain is relatively flat and open with minimal shade, so bring water and sun protection if spending time here.
A small pumping and generating plant inside the forebay itself can lift water an additional 50 feet (15 meters) when needed or operate in reverse to generate electricity. This dual-function facility operates only during peak demand periods, making it an example of flexible water infrastructure design.
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