Upper Oso
Key Takeaway
Upper Oso is classified as high hazard in California. It was completed in 1979 and is 47 years old. Its primary use is water supply. High hazard means loss of life is likely if the dam fails — it does not indicate the dam's current condition. Learn more.
Physical Details
| Dam Height | 142 ft (taller than 88.8% in CA) |
| Dam Length | 800 ft |
| Dam Type | Earth |
| Max Storage | 3.7K acre-ft |
| Surface Area | 115 acres |
| Drainage Area | 1 sq mi |
| Year Completed | 1979 (47 years old) |
| NID ID | CA01145 |
Safety Information
Loss of human life is likely if the dam fails.
Hazard potential describes downstream consequences of failure, not the dam's current condition. What does this mean?
Ownership
Santa Margarita Water District
Public Utility
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Low Hazard 98 ftFrequently Asked Questions
What is the hazard classification of Upper Oso?
Upper Oso is classified as High Hazard. Loss of human life is likely if the dam fails. This classification refers to the potential downstream consequences of a failure, not the dam's current structural condition.
Who owns and operates Upper Oso?
Upper Oso is owned by Santa Margarita Water District (Public Utility). The owner is responsible for maintenance, inspections, and compliance with dam safety regulations.
When was Upper Oso built?
Upper Oso was completed in 1979, making it 47 years old. Many U.S. dams were built between the 1930s and 1970s during a period of major infrastructure investment.
What is the primary purpose of Upper Oso?
Upper Oso serves the following purposes: Water Supply, Other, Irrigation. Many dams in the U.S. are multi-purpose, supporting flood control, water supply, recreation, and other uses.
How tall is Upper Oso?
Upper Oso has a dam height of 142 ft. Dam height is measured from the natural streambed at the downstream toe to the top of the dam, and may differ from the visible height.
When was Upper Oso last inspected?
Upper Oso was last inspected on October 26, 2021. Inspection dates indicate when a formal review occurred, not the results of that inspection.