Foss Valley
Foss Valley is an earth dam located in Napa County, California, built in 1988. It carries a High hazard potential classification and has a satisfactory condition assessment.
About Foss Valley
The primary purpose of Foss Valley 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 Atlas Peak Vineyards (private). It impounds the Tr Milliken Cr near N/a.
The dam stands 56 feet tall and stretches 2,500 feet across, creates a reservoir covering 31 acres, and has a maximum storage capacity of 800 acre-feet. Completed in 1988, the structure is 38 years 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 02/12/2025.
At 56 feet, this dam is taller than 94% 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 | Napa |
| Nearest City | N/a |
| River/Stream | Tr Milliken Cr |
| Coordinates | 38.42760, -122.27860 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 56 ft |
| Dam Height | 56 ft |
| Dam Length | 2,500 ft |
| Year Completed | 1988 (38 years old) |
Storage & Hydraulics
| NID Storage | 800 acre-ft |
| Max Storage | 800 acre-ft |
| Surface Area | 31 acres |
Ownership & Safety
| Purpose | Water Supply |
| Owner | Atlas Peak Vineyards |
| Owner Type | Private |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 02/12/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA01268 |
| Federal ID | CA01268 |
| More Info | State Dam Safety Program |