San Andreas
San Andreas is an earth dam located in San Mateo County, California, built in 1870. It carries a High hazard potential classification and has a fair condition assessment.
About San Andreas
The primary purpose of San Andreas 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 San Andreas Creek near San Mateo.
The dam stands 107 feet tall and stretches 727 feet across, creates a reservoir covering 550 acres, has a maximum storage capacity of 19,027 acre-feet, and collects water from a drainage area of 4 square miles. Completed in 1870, 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 fair — the dam has minor deficiencies that are being addressed or do not pose an immediate safety threat. An emergency action plan is in place for this dam. The most recent inspection on record was 11/20/2024.
At 107 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 | San Mateo |
| River/Stream | San Andreas Creek |
| Coordinates | 37.57980, -122.41290 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 107 ft |
| Dam Height | 107 ft |
| Dam Length | 727 ft |
| Year Completed | 1870 (156 years old) |
Storage & Hydraulics
| NID Storage | 19,027 acre-ft |
| Max Storage | 19,027 acre-ft |
| Surface Area | 550 acres |
| Drainage Area | 4 sq mi |
Ownership & Safety
| Purpose | Water Supply |
| Owner | City and County of San Francisco |
| Owner Type | Local Government |
| Hazard Classification | High |
| Condition Assessment | Fair |
| Last Inspection | 11/20/2024 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA00129 |
| Federal ID | CA00129 |
| More Info | State Dam Safety Program |