Big Sage is an earth dam located in Modoc County, California, built in 1921. It carries a High hazard potential classification and has a satisfactory condition assessment.
Dam profile
NID height · 49 ft49 ft tall and 680 ft long, taller than 92% 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 Big Sage
The primary purpose of Big Sage 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 Hot Spring Valley Water District (public utility). It impounds the Rattlesnake Cr near Alturas.
The dam stands 49 feet tall and stretches 680 feet across, creates a reservoir covering 5,270 acres, has a maximum storage capacity of 77,000 acre-feet, and collects water from a drainage area of 107 square miles. Completed in 1921, the structure is over a century 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. Notably, no emergency action plan is currently on file for this high-hazard dam. The most recent inspection on record was 04/22/2025.
At 49 feet, this dam is taller than 92% 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 | Modoc |
| Nearest City | Alturas |
| River/Stream | Rattlesnake Cr |
| Coordinates | 41.57780, -120.62770 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 49 ft |
| Dam Height | 49 ft |
| Dam Length | 680 ft |
| Year Completed | 1921 (105 years old) |
Storage & Hydraulics
| NID Storage | 77,000 acre-ft |
| Max Storage | 77,000 acre-ft |
| Surface Area | 5,270 acres |
| Drainage Area | 107 sq mi |
Ownership & Safety
| Purpose | Water Supply |
| Owner | Hot Spring Valley Water District |
| Owner Type | Public Utility |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 04/22/2025 |
| Emergency Action Plan | No |
Identifiers
| NID ID | CA00233 |
| Federal ID | CA00233 |
| More Info | State Dam Safety Program |