County Line Detention Dam
County Line Detention Dam is an earth dam located in Sierra County, New Mexico, built in 1956. It carries a High hazard potential classification and has a poor condition assessment.
About County Line Detention Dam
The primary purpose of County Line Detention Dam is flood risk reduction. The dam is designed to control downstream flooding by temporarily storing excess water during storms and releasing it at a controlled rate. The dam is owned by Caballo Soil & Water Conservation District (local government). It impounds the Rio Grande - Tr near Unincorporated Residents.
The dam stands 37 feet tall and stretches 650 feet across, has a maximum storage capacity of 182 acre-feet, and collects water from a drainage area of 1 square miles. Completed in 1956, 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 poor, meaning the dam has recognized safety deficiencies that require remediation to address risks. Notably, no emergency action plan is currently on file for this high-hazard dam. The most recent inspection on record was 06/02/2015. That was 10 years ago — unusually long for a high-hazard dam, which typically requires more frequent inspections.
At 37 feet, this dam is taller than 84% 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 New Mexico 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 | New Mexico |
| County | Sierra |
| Nearest City | Unincorporated Residents |
| River/Stream | Rio Grande - Tr |
| Coordinates | 32.78141, -107.26561 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 37 ft |
| Dam Height | 32 ft |
| Dam Length | 650 ft |
| Year Completed | 1956 (70 years old) |
Storage & Hydraulics
| NID Storage | 182 acre-ft |
| Max Storage | 182 acre-ft |
| Drainage Area | 1 sq mi |
| Max Discharge | 11,408 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Flood Risk Reduction |
| Owner | CABALLO SOIL & WATER CONSERVATION DISTRICT |
| Owner Type | Local Government |
| Hazard Classification | High |
| Condition Assessment | Poor |
| Last Inspection | 06/02/2015 |
| Emergency Action Plan | No |
Identifiers
| NID ID | NM00181 |
| Federal ID | NM00181 |
| More Info | State Dam Safety Program |