Green Oaks #1 is a privately owned earth dam located in San Mateo County, California, along Green Oaks Creek. Completed in 1936, the dam stands at 39 feet high and has a storage capacity of 322 acre-feet. Its primary purpose is flood risk reduction, with additional benefits including hydroelectric power generation and water supply.

The dam is regulated and inspected by the California Department of Water Resources under the Safety of Dams program. As of the last inspection in March 2021, the dam was deemed to have a low hazard potential and satisfactory condition. The surrounding area has a drainage area of 1.08 square miles and a surface area of 22 acres, providing essential protection against flooding for the community.

Overall, Green Oaks #1 serves as a vital infrastructure for water resource management in the region, contributing to flood control, water supply, and environmental protection along Green Oaks Creek. With a history dating back over 80 years, the dam continues to demonstrate its importance in safeguarding the surrounding area from potential risks associated with extreme weather events and climate change impacts.