Johnston
California — San Mateo County — Arroyo Leon
Location
| State | California |
| County | San Mateo |
| River | Arroyo Leon |
| Coordinates | 37.45410, -122.42390 |
Physical Characteristics
| NID Height | 31 ft |
| Dam Height | 31 ft |
| Dam Length | 132 ft |
| NID Storage | 30 acre-ft |
| Max Storage | 30 acre-ft |
| Surface Area | 5 acres |
Safety Classification
| Hazard Potential | Low |
| Condition Assessment | Satisfactory |
| EAP Status | No |
| Last Inspection | January 6, 2026 |
| Inspection Frequency | 0.5 |
Dam Information
| Year Completed | 1919 |
| Primary Purpose | Water Supply |
| Dam Type | Gravity |
| Owner Type | Private |
| Owner | Peninsula Open Space Trust |
Location Map
About This Dam Record
Dam safety data is maintained by the Army Corps of Engineers National Inventory of Dams (NID). High-hazard dams are those where failure could cause loss of life or major property damage downstream.