Lower Peak Lake Auxiliary Reservoir Report

Last Updated: December 5, 2025

Lower Peak Lake Auxiliary is a private hydroelectric dam located in Placer County, California, near the town of Washington.


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Summary

Built in 1860, this earth dam stands at a height of 7 feet and has a hydraulic height of 3.5 feet. With a storage capacity of 484 acre-feet, the dam serves the primary purpose of hydroelectric power generation and is regulated by the Federal Energy Regulatory Commission.

Situated on the South Yuba River, Lower Peak Lake Auxiliary has a surface area of 33.3 acres and a maximum discharge of 312 cubic feet per second. The dam features an uncontrolled spillway with a width of 55 feet and has a low hazard potential. Although the condition assessment is not available, the risk assessment is moderate, with a risk level of 3. Emergency action plans have been prepared and last revised in December 2020, ensuring that the dam is well-prepared for any potential hazards.

Overall, Lower Peak Lake Auxiliary is a historic structure with a vital role in providing hydroelectric power to the region. Its location in the picturesque surroundings of Placer County makes it a significant landmark for water resource and climate enthusiasts interested in the sustainable development of water infrastructure in California.

Year Completed

1860

Dam Length

410

Dam Height

7

River Or Stream

South Yuba River - Tr

Primary Dam Type

Earth

Surface Area

33.3

Hydraulic Height

3.5

Drainage Area

1

Nid Storage

484

Structural Height

7

Hazard Potential

Low

Nid Height

7
       
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.