Located in San Diego, California, the San Marcos dam stands as a vital water supply structure in the region. Built in 1958, this earth dam spans 400 feet in length and reaches a height of 85 feet, with a storage capacity of 320 acre-feet. Serving multiple purposes including irrigation and water supply, the dam is situated on the Tr San Marcos Creek, contributing to the overall water management system in the area.

Managed by a public utility, the San Marcos dam is regulated by the Department of Water Resources (DWR) and falls under the Safety of Dams jurisdiction. With a high hazard potential but currently deemed to be in satisfactory condition, the dam undergoes regular inspections and enforcement measures to ensure the safety and functionality of the structure. The last assessment in September 2017 confirmed its sound state, providing assurance to the surrounding community in Los Vallecitos.

Despite its age, the San Marcos dam continues to play a crucial role in water resource management in the region, with a close eye on its maintenance and emergency preparedness. As a key component in the water supply infrastructure, the dam serves as a reminder of the importance of sustainable water management practices, particularly in the face of changing climate patterns and increasing water demands.