Preston Forebay is an earth dam located in Amador County, California, built in 1892. It carries a Low hazard potential classification and has a satisfactory condition assessment.
Dam profile
NID height · 40 ft40 ft tall and 176 ft long, taller than 86% of U.S. dams with a recorded height. Height is drawn to scale against a two-story house, about 25 ft; the profile is a generic embankment section and the water level is illustrative.
About Preston Forebay
Preston Forebay is a dam in Amador, California. The dam is owned by Amador Regional Sanitation Authority (public utility). It impounds the Offstream.
The dam stands 40 feet tall and stretches 176 feet across, creates a reservoir covering 2 acres, and has a maximum storage capacity of 30 acre-feet. Completed in 1892, the structure is over a century old.
This dam has a low hazard potential classification, meaning that failure would cause minimal damage, limited primarily to the dam owner's property, with no expected loss of life. Its condition is rated satisfactory, indicating no existing or potential dam safety deficiencies are recognized. The most recent inspection on record was 11/24/2025.
At 40 feet, this dam is taller than 86% of dams nationwide.
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Location
| State | California |
| County | Amador |
| River/Stream | Offstream |
| Coordinates | 38.37540, -120.92330 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 40 ft |
| Dam Height | 40 ft |
| Dam Length | 176 ft |
| Year Completed | 1892 (134 years old) |
Storage & Hydraulics
| NID Storage | 30 acre-ft |
| Max Storage | 30 acre-ft |
| Surface Area | 2 acres |
Ownership & Safety
| Purpose | Other |
| Owner | Amador Regional Sanitation Authority |
| Owner Type | Public Utility |
| Hazard Classification | Low |
| Condition Assessment | Satisfactory |
| Last Inspection | 11/24/2025 |
| Emergency Action Plan | No |
Identifiers
| NID ID | CA00006 |
| Federal ID | CA00006 |
| More Info | State Dam Safety Program |