Mammoth Reservoir Reservoir Report

Last Updated: December 5, 2025

Mammoth Reservoir, located in Loomis, California, is a local government-owned water resource primarily used for hydroelectric power generation and irrigation purposes.


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Summary

Built in 1851, this offstream earth dam stands at a height of 23 feet and has a capacity of 103 acre-feet. With a surface area of 11 acres and a drainage area of 0.02 square miles, the reservoir serves as a crucial water management structure in the region.

Managed by the California Department of Water Resources, Mammoth Reservoir has a high hazard potential but is deemed to be in satisfactory condition following a recent assessment in September 2017. The dam is subject to regular inspections, with the last one conducted in February 2021. Despite its age, Mammoth Reservoir continues to play a vital role in water supply and energy production in the area, showcasing the resilience and importance of historical water infrastructure in the face of changing climate conditions.

As a key component of the local water infrastructure, Mammoth Reservoir reflects the intersection of history, hydroelectric power, and water management in California. With its long-standing presence and continued functionality, the reservoir stands as a testament to the enduring value of water resources in the region. Climate enthusiasts and water resource professionals alike can appreciate the significance of Mammoth Reservoir in sustaining the needs of both the community and the environment in an ever-changing climate landscape.

Year Completed

1851

Dam Length

2360

Dam Height

23

River Or Stream

Offstream

Primary Dam Type

Earth

Surface Area

11

Hydraulic Height

19.4

Drainage Area

0.02

Nid Storage

103

Hazard Potential

High

Nid Height

23
       
Seasonal Comparison

Weather Forecast

Dam Data Reference

Condition Assessment

Satisfactory
No existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
Fair
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
Poor A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Investigations and studies are necessary.
Unsatisfactory
A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
Not Rated
The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Not Available
Dams for which the condition assessment is restricted to approved government users.

Hazard Potential Classification

High
Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
Significant
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
Low
Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
Undetermined
Dams for which a downstream hazard potential has not been designated or is not provided.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.