Big Dalton
Big Dalton is a multi-arch dam located in Los Angeles County, California, built in 1929. It carries a High hazard potential classification and has a satisfactory condition assessment.
About Big Dalton
The primary purpose of Big Dalton 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 Big Dalton Wash near Glendora.
The dam stands 153 feet tall and stretches 480 feet across, creates a reservoir covering 26 acres, has a maximum storage capacity of 1,290 acre-feet, and collects water from a drainage area of 4 square miles. Completed in 1929, 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 12/02/2025.
At 153 feet, this dam is taller than 99% 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 | Glendora |
| River/Stream | Big Dalton Wash |
| Coordinates | 34.17040, -117.80990 |
Physical Characteristics
| Dam Type | Multi-Arch |
| NID Height | 153 ft |
| Dam Height | 153 ft |
| Dam Length | 480 ft |
| Year Completed | 1929 (97 years old) |
Storage & Hydraulics
| NID Storage | 1,290 acre-ft |
| Max Storage | 1,290 acre-ft |
| Surface Area | 26 acres |
| Drainage Area | 4 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 | 12/02/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA00187 |
| Federal ID | CA00187 |
| More Info | State Dam Safety Program |