Johnston
Low HazardSatisfactory ConditionEmergency Action Plan: No
Location
| County | San Mateo |
| River/Stream | Arroyo Leon |
| Coordinates | 37.45410, -122.42390 |
Physical Characteristics
| Dam Type | Gravity |
| NID Height | 31 ft |
| Dam Height | 31 ft |
| Dam Length | 132 ft |
| Year Completed | 1919 (107 years old) |
Storage & Hydraulics
| NID Storage | 30 acre-ft |
| Max Storage | 30 acre-ft |
| Surface Area | 5 acres |
| Drainage Area | 7 sq mi |
Ownership & Safety
| Purpose | Water Supply |
| Owner | Peninsula Open Space Trust |
| Owner Type | Private |
| Hazard Classification | Low |
| Condition Assessment | Satisfactory |
| Last Inspection | 01/06/2026 |
| Emergency Action Plan | No |