Pilarcitos
Pilarcitos is an earth dam located in San Mateo County, California, built in 1866. It carries a High hazard potential classification and has a poor condition assessment.
About Pilarcitos
The primary purpose of Pilarcitos is water supply. The dam stores water for municipal, industrial, or agricultural use, helping ensure a reliable supply for the surrounding area. The dam is owned by City And County Of San Francisco (local government). It impounds the Pilarcitos Crk near Half Moon Bay.
The dam stands 103 feet tall and stretches 520 feet across, creates a reservoir covering 109 acres, has a maximum storage capacity of 3,100 acre-feet, and collects water from a drainage area of 3 square miles. Completed in 1866, the structure is one of the older dams in the region, with over a century and a half of service.
This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. Its condition is rated poor, meaning the dam has recognized safety deficiencies that require remediation to address risks. An emergency action plan is in place for this dam. The most recent inspection on record was 04/29/2025.
At 103 feet, this dam is taller than 98% of all dams in the United States.
Living Downstream
If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The California dam safety program can provide more specific information about emergency planning for this structure.
Search for dams near your address to see all dams in your area with hazard classifications and safety data.
Location
| State | California |
| County | San Mateo |
| Nearest City | Half Moon Bay |
| River/Stream | Pilarcitos Crk |
| Coordinates | 37.54720, -122.42330 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 103 ft |
| Dam Height | 103 ft |
| Dam Length | 520 ft |
| Year Completed | 1866 (160 years old) |
Storage & Hydraulics
| NID Storage | 3,100 acre-ft |
| Max Storage | 3,100 acre-ft |
| Surface Area | 109 acres |
| Drainage Area | 3 sq mi |
| Max Discharge | 1,244 cfs |
Ownership & Safety
| Purpose | Water Supply |
| Owner | City and County of San Francisco |
| Owner Type | Local Government |
| Hazard Classification | High |
| Condition Assessment | Poor |
| Last Inspection | 04/29/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA00128 |
| Federal ID | CA00128 |
| More Info | State Dam Safety Program |