Big Johnson
Big Johnson is an earth dam located in Modoc County, California, built in 1959. It carries a Low hazard potential classification and has a satisfactory condition assessment.
About Big Johnson
The primary purpose of Big Johnson 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 Stanley Johnson (private). It impounds the Tr Lost River.
The dam stands 18 feet tall and stretches 1,900 feet across, creates a reservoir covering 65 acres, has a maximum storage capacity of 410 acre-feet, and collects water from a drainage area of 3 square miles. Completed in 1959, the structure is well into its service life at over 50 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 05/29/2025.
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Location
| State | California |
| County | Modoc |
| River/Stream | Tr Lost River |
| Coordinates | 41.94580, -121.21960 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 18 ft |
| Dam Height | 18 ft |
| Dam Length | 1,900 ft |
| Year Completed | 1959 (67 years old) |
Storage & Hydraulics
| NID Storage | 410 acre-ft |
| Max Storage | 410 acre-ft |
| Surface Area | 65 acres |
| Drainage Area | 3 sq mi |
Ownership & Safety
| Purpose | Water Supply |
| Owner | Stanley Johnson |
| Owner Type | Private |
| Hazard Classification | Low |
| Condition Assessment | Satisfactory |
| Last Inspection | 05/29/2025 |
| Emergency Action Plan | No |
Identifiers
| NID ID | CA00918 |
| Federal ID | CA00918 |
| More Info | State Dam Safety Program |