Upper Twin Lake
Upper Twin Lake is an earth dam located in Napa County, California, built in 1987. It carries a Low hazard potential classification and has a satisfactory condition assessment.
About Upper Twin Lake
The primary purpose of Upper Twin Lake 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 Juliana Mutual Water Company (private). It impounds the Tr Pope Creek.
The dam stands 19 feet tall and stretches 350 feet across, creates a reservoir covering 6 acres, and has a maximum storage capacity of 63 acre-feet. Completed in 1987, the structure is 39 years 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 01/30/2025.
Search for dams near your address to see all dams in your area with hazard classifications and safety data.
Location
| State | California |
| County | Napa |
| River/Stream | Tr Pope Creek |
| Coordinates | 38.64640, -122.42050 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 19 ft |
| Dam Height | 19 ft |
| Dam Length | 350 ft |
| Year Completed | 1987 (39 years old) |
Storage & Hydraulics
| NID Storage | 63 acre-ft |
| Max Storage | 63 acre-ft |
| Surface Area | 6 acres |
Ownership & Safety
| Purpose | Water Supply |
| Owner | Juliana Mutual Water Company |
| Owner Type | Private |
| Hazard Classification | Low |
| Condition Assessment | Satisfactory |
| Last Inspection | 01/30/2025 |
| Emergency Action Plan | No |
Identifiers
| NID ID | CA01294 |
| Federal ID | CA01294 |
| More Info | State Dam Safety Program |