San Marcos, also known as Lake San Marcos, is a private dam located in Leucadia, California. This dam plays a vital role in flood risk reduction along the San Marcos Creek, with a primary purpose of protecting the surrounding area from potential flooding. Built in 1946, this arch dam stands at 52 feet tall and has a storage capacity of 480 acre-feet, serving as a key infrastructure for irrigation and water supply in the region.

Managed by the California Department of Water Resources (DWR) under the Safety of Dams program, San Marcos Dam is regulated, permitted, inspected, and enforced to ensure its structural integrity and safety. With a high hazard potential but assessed as satisfactory in condition, the dam undergoes regular inspections to maintain its functionality. In case of emergencies, protocols are in place, although details on the Emergency Action Plan (EAP) readiness and risk management measures are not specified in the available data. Water resource and climate enthusiasts would find San Marcos Dam an interesting case study in dam infrastructure and flood risk management in Southern California.