San Marcos Dam, located in San Luis Obispo, California, was completed in 1964 and serves multiple purposes including flood risk reduction, irrigation, and water supply. Owned privately, the dam stands at 42 feet high with a hydraulic height of 32 feet, holding a storage capacity of 325 acre-feet. Its primary source agency is the Natural Resources Conservation Service, and it is regulated by the California Department of Water Resources for safety compliance.

The dam is situated on San Marcos Creek, with a drainage area of 7.9 square miles and a surface area of 29 acres. With a significant hazard potential but a satisfactory condition assessment as of September 2017, the dam undergoes regular inspections to ensure its structural integrity. The surrounding area, including the city of Paso Robles, benefits from the dam's flood risk mitigation efforts and water supply management, making it a crucial infrastructure for local water resource and climate enthusiasts to monitor and appreciate.