O`shaughnessy is a gravity dam located in Tuolumne County, California, built in 1923. It carries a High hazard potential classification and has a satisfactory condition assessment.
Dam profile
NID height · 312 ft312 ft tall and 900 ft long, taller than 99% of U.S. dams with a recorded height. Height is drawn to scale against the Statue of Liberty, 305 ft ground to torch; the profile is a generic concrete gravity section and the water level is illustrative.
About O`shaughnessy
The primary purpose of O`shaughnessy 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 San Francisco Public Utilities Commission (local government). It impounds the Tuolumne River near Waterford.
The dam stands 312 feet tall and stretches 900 feet across, creates a reservoir covering 1,972 acres, has a maximum storage capacity of 360,000 acre-feet, and collects water from a drainage area of 459 square miles. Completed in 1923, the structure is over a century old.
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 10/06/2025.
At 312 feet, this dam is taller than 99% 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 | Tuolumne |
| Nearest City | Waterford |
| River/Stream | Tuolumne River |
| Coordinates | 37.94840, -119.78900 |
Physical Characteristics
| Dam Type | Gravity |
| NID Height | 312 ft |
| Dam Height | 312 ft |
| Dam Length | 900 ft |
| Year Completed | 1923 (103 years old) |
Storage & Hydraulics
| NID Storage | 360,000 acre-ft |
| Max Storage | 360,000 acre-ft |
| Surface Area | 1,972 acres |
| Drainage Area | 459 sq mi |
Ownership & Safety
| Purpose | Water Supply |
| Owner | San Francisco Public Utilities Commission |
| Owner Type | Local Government |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 10/06/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA00123 |
| Federal ID | CA00123 |
| More Info | State Dam Safety Program |