Circle S is an earth dam located in Napa County, California, built in 1979. It carries a High hazard potential classification and has a satisfactory condition assessment.
Dam profile
NID height · 28 ft28 ft tall and 412 ft long, taller than 62% 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 Circle S
The primary purpose of Circle S 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 Circle R Ranch LLC (private). It impounds the Tr Milliken Cr near Dam Owner's Home.
The dam stands 28 feet tall and stretches 412 feet across, creates a reservoir covering 9 acres, has a maximum storage capacity of 131 acre-feet, and collects water from a drainage area of 0 square miles. Completed in 1979, the structure is 47 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.
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 | Dam Owner's Home |
| River/Stream | Tr Milliken Cr |
| Coordinates | 38.41930, -122.27120 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 28 ft |
| Dam Height | 28 ft |
| Dam Length | 412 ft |
| Year Completed | 1979 (47 years old) |
Storage & Hydraulics
| NID Storage | 131 acre-ft |
| Max Storage | 131 acre-ft |
| Surface Area | 9 acres |
| Drainage Area | 0 sq mi |
Ownership & Safety
| Purpose | Water Supply |
| Owner | Circle R Ranch LLC |
| Owner Type | Private |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 02/12/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA01141 |
| Federal ID | CA01141 |
| More Info | State Dam Safety Program |