Blanchard-offner is an earth dam located in Napa County, California, built in 1963. It carries a High hazard potential classification and has a satisfactory condition assessment.
Dam profile
NID height · 47 ft47 ft tall and 785 ft long, taller than 91% of U.S. dams with a recorded height. Height is drawn to scale against a ten-story building, about 100 ft; the profile is a generic embankment section and the water level is illustrative.
About Blanchard-offner
Blanchard-offner is a dam in Napa, California. The dam is owned by Jim Collins (private). It impounds the Tr Pope Creek near N/a.
The dam stands 47 feet tall and stretches 785 feet across, creates a reservoir covering 19 acres, and has a maximum storage capacity of 274 acre-feet. Completed in 1963, the structure is well into its service life at over 50 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 11/04/2025.
At 47 feet, this dam is taller than 91% 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 Pope Creek |
| Coordinates | 38.63730, -122.46580 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 47 ft |
| Dam Height | 47 ft |
| Dam Length | 785 ft |
| Year Completed | 1963 (63 years old) |
Storage & Hydraulics
| NID Storage | 274 acre-ft |
| Max Storage | 274 acre-ft |
| Surface Area | 19 acres |
Ownership & Safety
| Purpose | Other |
| Owner | Jim Collins |
| Owner Type | Private |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 11/04/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA01037 |
| Federal ID | CA01037 |
| More Info | State Dam Safety Program |