Gem Lake
Gem Lake is a concrete dam located in Mono County, California, built in 1917. It carries a High hazard potential classification and has a poor condition assessment.
About Gem Lake
The primary purpose of Gem Lake is hydroelectric. The dam generates hydroelectric power by channeling water through turbines, converting the energy of flowing water into electricity. The dam is owned by Southern California Edison Company (private). It impounds the Rush Creek near June Lake.
The dam stands 80 feet tall and stretches 688 feet across, creates a reservoir covering 282 acres, has a maximum storage capacity of 17,228 acre-feet, and collects water from a drainage area of 21 square miles. Completed in 1917, the structure is over a century 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 poor, meaning the dam has recognized safety deficiencies that require remediation to address risks. An emergency action plan is in place for this dam. The most recent inspection on record was 08/20/2025.
At 80 feet, this dam is taller than 97% 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 | Mono |
| Nearest City | June Lake |
| River/Stream | Rush Creek |
| Coordinates | 37.75110, -119.14140 |
Physical Characteristics
| Dam Type | Concrete |
| NID Height | 80 ft |
| Dam Height | 80 ft |
| Dam Length | 688 ft |
| Year Completed | 1917 (109 years old) |
Storage & Hydraulics
| NID Storage | 17,228 acre-ft |
| Max Storage | 17,228 acre-ft |
| Normal Storage | 17,228 acre-ft |
| Surface Area | 282 acres |
| Drainage Area | 21 sq mi |
| Max Discharge | 1,700 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Hydroelectric |
| Owner | Southern California Edison Company |
| Owner Type | Private |
| Hazard Classification | High |
| Condition Assessment | Poor |
| Last Inspection | 08/20/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA00453 |
| Federal ID | CA00453 |
| More Info | State Dam Safety Program |