San Marcos Reservoir Report

Last Updated: December 5, 2025

San Marcos, also known as Lake San Marcos, is a private dam located in Leucadia, California.


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Summary

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.

Year Completed

1946

Dam Length

290

Dam Height

52

River Or Stream

San Marcos Creek

Primary Dam Type

Arch

Surface Area

54

Hydraulic Height

42

Drainage Area

29

Nid Storage

480

Hazard Potential

High

Nid Height

52
       
Seasonal Comparison

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Dam Data Reference

Condition Assessment

Satisfactory
No existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
Fair
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
Poor A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Investigations and studies are necessary.
Unsatisfactory
A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
Not Rated
The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Not Available
Dams for which the condition assessment is restricted to approved government users.

Hazard Potential Classification

High
Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
Significant
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
Low
Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
Undetermined
Dams for which a downstream hazard potential has not been designated or is not provided.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.