Lopez is an earth dam located in San Luis Obispo County, California, built in 1969. It carries a High hazard potential classification and has a satisfactory condition assessment.
Dam profile
NID height · 166 ft166 ft tall and 1,120 ft long, taller than 99% of U.S. dams with a recorded height. Height is drawn to scale against the Statue of Liberty, 305 ft ground to torch; the profile is a generic embankment section and the water level is illustrative.
About Lopez
The primary purpose of Lopez 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 San Luis Obispo County Flood Control and Water Conservation District (local government). It impounds the Arroyo Grande Cr near Arroyo Grande.
The dam stands 166 feet tall and stretches 1,120 feet across, creates a reservoir covering 950 acres, has a maximum storage capacity of 52,500 acre-feet, and collects water from a drainage area of 68 square miles. Completed in 1969, 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 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 01/29/2025.
At 166 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 | San Luis Obispo |
| Nearest City | Arroyo Grande |
| River/Stream | Arroyo Grande Cr |
| Coordinates | 35.18870, -120.48920 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 166 ft |
| Dam Height | 166 ft |
| Dam Length | 1,120 ft |
| Year Completed | 1969 (57 years old) |
Storage & Hydraulics
| NID Storage | 52,500 acre-ft |
| Max Storage | 52,500 acre-ft |
| Surface Area | 950 acres |
| Drainage Area | 68 sq mi |
Ownership & Safety
| Purpose | Water Supply |
| Owner | San Luis Obispo County Flood Control and Water Conservation District |
| Owner Type | Local Government |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 01/29/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA00887 |
| Federal ID | CA00887 |
| More Info | State Dam Safety Program |