Mill Pond Reservoir Report

Last Updated: December 5, 2025

Mill Pond, located in Marin County, California, is a federal-owned structure managed by the National Park Service.


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Summary

Built in 1956, this Earth dam stands at a height of 20 feet and spans 280 feet in length, with a storage capacity of 21 acre-feet. The pond covers an area of 5.5 acres and serves as a significant water resource in the region. While the dam has a spillway width of 1 foot, it does not have any associated locks or drainage area.

Despite its age, the condition assessment of Mill Pond is marked as "Not Available" with a significant hazard potential. The last inspection conducted was in June 2014, with an inspection frequency of 0. The Emergency Action Plan (EAP) was last revised in June 2017, and the structure meets guidelines for emergency preparedness. With its location in the San Francisco District and under the jurisdiction of the National Park Service, Mill Pond remains a key component of the water infrastructure in the area, attracting enthusiasts interested in water resources and climate management.

Year Completed

1956

Dam Length

280

Dam Height

20

Primary Dam Type

Earth

Surface Area

5.5

Nid Storage

21

Hazard Potential

Significant

Nid Height

20
       
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.