Mcmahon Reservoir Report

Last Updated: December 5, 2025

Mcmahon is a private earth dam located in Snelling, California, along Maxwell Creek.


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Summary

Built in 1957, this dam serves primarily for water supply, with a storage capacity of 520 acre-feet. It stands at a height of 52 feet and has a hydraulic height of 42 feet, making it a crucial structure for irrigation and water supply in the area.

Managed by the California Department of Water Resources, Mcmahon is regulated, permitted, inspected, and enforced by state agencies to ensure its safety and compliance with regulations. Despite its low hazard potential, the dam is regularly assessed and deemed to be in satisfactory condition. The last inspection in August 2019 confirmed its structural integrity, making it a reliable resource for water management and climate resilience in Mariposa County.

With its strategic location and vital role in water supply, Mcmahon represents a valuable asset for the community and the environment. As a key structure along Maxwell Creek, this dam not only provides essential water resources but also contributes to the overall sustainability and resilience of the region. Its satisfactory condition and low hazard potential underscore the importance of proper maintenance and monitoring to ensure its continued functionality and safety for years to come.

Year Completed

1957

Dam Length

705

Dam Height

52

River Or Stream

Maxwell Creek

Primary Dam Type

Earth

Surface Area

26

Hydraulic Height

42

Drainage Area

18.2

Nid Storage

520

Hazard Potential

Low

Nid Height

52
       
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.