Upper Letts Reservoir Report

Last Updated: December 5, 2025

Upper Letts is a federal dam located in Stonyford, California, along Letts Creek.


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Summary

Built in 1958 by the USDA Forest Service, this earth dam stands at 21 feet high with a hydraulic height of 26 feet, serving primarily for recreation purposes. With a storage capacity of 319 acre-feet, Upper Letts offers a serene environment for water resource and climate enthusiasts to enjoy various water-related activities.

Despite its small drainage area and uncontrolled spillway type, Upper Letts poses a high hazard potential with a moderate risk assessment rating. Currently, the dam's condition remains unrated, with the last inspection conducted in June 2014 by the Forest Service. While emergency preparedness measures have not been specified, the dam's risk management strategies and inundation maps readiness are unknown, highlighting the need for proactive monitoring and maintenance to ensure the safety of the surrounding community and recreational users.

As part of the San Francisco District, Upper Letts is closely regulated and operated by the Forest Service, emphasizing the importance of continued oversight and adherence to safety guidelines. With its picturesque location and potential risks, Upper Letts serves as a reminder of the delicate balance between utilizing water resources for recreation while safeguarding against potential hazards in the face of changing climate patterns and environmental conditions.

Year Completed

1958

Dam Length

212

Dam Height

21

River Or Stream

LETTS CREEK

Primary Dam Type

Earth

Hydraulic Height

26

Nid Storage

319

Structural Height

21

Hazard Potential

High

Nid Height

26
       
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.