Lyons Reservoir Report

Last Updated: December 24, 2025

Located in Tuolumne County, California, Lyons is a private hydroelectric dam on the South Fork Stanislaus River.


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Summary

Completed in 1930, this concrete arch dam stands at a height of 132 feet and spans 535 feet in length, providing essential services such as fire protection, irrigation, and hydroelectric power generation. With a maximum storage capacity of 6,228 acre-feet and a drainage area of 66.8 square miles, Lyons plays a crucial role in managing water resources in the region.

Managed by the Federal Energy Regulatory Commission, Lyons has a controlled spillway width of 284 feet and four Tainter radial gates. The dam's hazard potential is classified as high, with a very high risk assessment rating. While the condition assessment is not available, regular inspections and enforcement by state agencies ensure its operational safety and compliance with regulations. As a key structure in the water infrastructure of California, Lyons exemplifies the intersection of water resource management and climate resilience in the face of varying environmental challenges.

The dam's location in Long Barn, California, and its role in the conservation of water resources highlight the importance of sustainable practices and infrastructure investment in mitigating the impacts of climate change. With its historical significance and continued operation under state jurisdiction, Lyons stands as a testament to the ongoing efforts to balance water resource utilization with environmental conservation in the face of evolving climate patterns. For water resource and climate enthusiasts, Lyons offers a fascinating case study in the intersection of engineering, policy, and environmental stewardship.

Year Completed

1930

Dam Length

535

Dam Height

132

River Or Stream

South Fork Stanislaus River

Primary Dam Type

Concrete

Surface Area

184

Drainage Area

66.8

Nid Storage

6228

Outlet Gates

Tainter (radial) - 4

Hazard Potential

High

Nid Height

132
       
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.