Mccoy Flat
Mccoy Flat is an earth dam located in Lassen County, California, built in 1891. It carries a Low hazard potential classification and has a satisfactory condition assessment.
About Mccoy Flat
The primary purpose of Mccoy Flat 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 Lassen Irrigation Company (private). It impounds the Susan River.
The dam stands 21 feet tall and stretches 650 feet across, creates a reservoir covering 1,800 acres, has a maximum storage capacity of 17,290 acre-feet, and collects water from a drainage area of 110 square miles. Completed in 1891, the structure is over a century 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 08/27/2025.
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Location
| State | California |
| County | Lassen |
| River/Stream | Susan River |
| Coordinates | 40.45370, -120.94310 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 21 ft |
| Dam Height | 21 ft |
| Dam Length | 650 ft |
| Year Completed | 1891 (135 years old) |
Storage & Hydraulics
| NID Storage | 17,290 acre-ft |
| Max Storage | 17,290 acre-ft |
| Surface Area | 1,800 acres |
| Drainage Area | 110 sq mi |
Ownership & Safety
| Purpose | Water Supply |
| Owner | Lassen Irrigation Company |
| Owner Type | Private |
| Hazard Classification | Low |
| Condition Assessment | Satisfactory |
| Last Inspection | 08/27/2025 |
| Emergency Action Plan | No |
Identifiers
| NID ID | CA00517 |
| Federal ID | CA00517 |
| More Info | State Dam Safety Program |