Pilarcitos Reservoir Report

Last Updated: December 5, 2025

Pilarcitos, also known as Pilarcitos Lake, is a vital water resource located in Half Moon Bay, California.


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Summary

Owned by the local government, this dam on Pilarcitos Creek was completed in 1866 and serves the primary purpose of water supply. With a height of 103 feet and a hydraulic height of 95.8 feet, Pilarcitos Dam has a storage capacity of 3100 acre-feet and covers a surface area of 109 acres.

Managed by the Department of Water Resources and regulated by the Safety of Dams agency, Pilarcitos Dam is considered to have a high hazard potential but is currently rated as being in satisfactory condition. The last inspection in December 2020 confirmed its structural integrity, and regular inspections are conducted to ensure the safety of the surrounding community. While the dam meets state permitting and enforcement standards, there is no information available on emergency action plans or risk assessment measures for this crucial water source.

Water resource and climate enthusiasts will be intrigued by the historical significance and technical specifications of Pilarcitos Dam. Its location in San Mateo County, California, and its association with Pilarcitos Creek make it a key component of the region's water infrastructure. As a critical water supply source, the dam's condition and regulatory oversight are essential factors in ensuring reliable water access for the surrounding area. Further exploration into the emergency preparedness and risk management aspects of Pilarcitos Dam could provide valuable insights into water resource resilience in the face of climate challenges.

Year Completed

1866

Dam Length

520

Dam Height

103

River Or Stream

Pilarcitos Crk

Primary Dam Type

Earth

Surface Area

109

Hydraulic Height

95.8

Drainage Area

3.8

Nid Storage

3100

Hazard Potential

High

Nid Height

103
       
Seasonal Comparison

Weather Forecast

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.