San Diego Reservoir
San Diego Reservoir is an earth dam located in Tuolumne County, California, built in 1860. It carries a High hazard potential classification and has a satisfactory condition assessment.
About San Diego Reservoir
The primary purpose of San Diego Reservoir 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 Yosemite Community College District (public utility). It impounds the Tr Mormon Cr near Columbia.
The dam stands 39 feet tall and stretches 155 feet across, creates a reservoir covering 5 acres, has a maximum storage capacity of 40 acre-feet, and collects water from a drainage area of 0 square miles. Completed in 1860, 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 satisfactory, indicating no existing or potential dam safety deficiencies are recognized. An emergency action plan is in place for this dam. The most recent inspection on record was 09/16/2025.
At 39 feet, this dam is taller than 86% of dams nationwide.
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 | Tuolumne |
| Nearest City | Columbia |
| River/Stream | Tr Mormon Cr |
| Coordinates | 38.03050, -120.38980 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 39 ft |
| Dam Height | 39 ft |
| Dam Length | 155 ft |
| Year Completed | 1860 (166 years old) |
Storage & Hydraulics
| NID Storage | 40 acre-ft |
| Max Storage | 40 acre-ft |
| Surface Area | 5 acres |
| Drainage Area | 0 sq mi |
Ownership & Safety
| Purpose | Water Supply |
| Owner | Yosemite Community College District |
| Owner Type | Public Utility |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 09/16/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA00900 |
| Federal ID | CA00900 |
| More Info | State Dam Safety Program |