Grayhorse Detention Dam Reservoir Report

Last Updated: December 5, 2025

Grayhorse Detention Dam, located in Duncan, Arizona, was completed in 1956 by the Bureau of Land Management with a primary purpose of flood risk reduction along the Round Mountain Draw tributary.


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Summary

This gravity dam stands at an impressive 28 feet in structural height and has a hydraulic height of 23 feet, with a length of 603 feet. With a capacity to hold 120 acre-feet of water, the dam serves to protect the surrounding area from potential flood hazards, with a low hazard potential and fair condition assessment.

Despite being owned, funded, designed, and regulated by the Bureau of Land Management, Grayhorse Detention Dam does not fall under state jurisdiction or regulation. This federal-owned structure operates without state permitting, inspection, or enforcement. With a moderate risk assessment rating of 3, the dam has an inspection frequency of 5 years and was last assessed in August 2015. While the dam has not been modified since its completion, it continues to serve as a vital tool in managing flood risks in the Greenlee County area.

Year Completed

1956

Dam Length

603

River Or Stream

ROUND MOUNTAIN DRAW TRIBUTARY

Primary Dam Type

Gravity

Surface Area

20

Hydraulic Height

23

Nid Storage

120

Structural Height

28

Hazard Potential

Low

Foundations

Unlisted/Unknown

Nid Height

28
       
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.