Thompson Creek
Thompson Creek is an earth dam located in Los Angeles County, California, built in 1928. It carries a High hazard potential classification and has a satisfactory condition assessment.
About Thompson Creek
The primary purpose of Thompson Creek 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 Los Angeles County Department Of Public Works (local government). It impounds the Thompson Creek near Claremont, Ca.
The dam stands 66 feet tall and stretches 1,500 feet across, creates a reservoir covering 345 acres, has a maximum storage capacity of 543 acre-feet, and collects water from a drainage area of 3 square miles. Completed in 1928, the structure is well-established, with more than 75 years of service.
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 10/22/2025.
At 66 feet, this dam is taller than 96% of all dams in the United States.
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 | Los Angeles |
| Nearest City | Claremont, Ca |
| River/Stream | Thompson Creek |
| Coordinates | 34.14070, -117.71380 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 66 ft |
| Dam Height | 66 ft |
| Dam Length | 1,500 ft |
| Year Completed | 1928 (98 years old) |
Storage & Hydraulics
| NID Storage | 543 acre-ft |
| Max Storage | 543 acre-ft |
| Surface Area | 345 acres |
| Drainage Area | 3 sq mi |
Ownership & Safety
| Purpose | Flood Risk Reduction |
| Owner | Los Angeles County Department Of Public Works |
| Owner Type | Local Government |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 10/22/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA00198 |
| Federal ID | CA00198 |
| More Info | State Dam Safety Program |