Mary Stock Reservoir Report
Nearby: Mary No. 2 Kimberly
Last Updated: December 5, 2025
Mary Stock is a private earth dam located in Johnson County, Wyoming, near the city of Arvada.
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Summary
Built in 1970 for fire protection, stock, or small fish pond purposes, this dam stands at 38 feet tall with a hydraulic height of 33 feet. With a storage capacity of 87 acre-feet and a surface area of 7 acres, Mary Stock plays a crucial role in water resource management in the region.
Despite its important function, the dam's condition assessment is rated as poor, with a low hazard potential. The last inspection in September 2017 indicated a need for improvements to ensure its structural integrity and long-term effectiveness. Although the risk assessment categorizes it as moderate, with a risk management plan in place, continued monitoring and maintenance are essential to mitigate any potential hazards and safeguard the surrounding area from flooding or other water-related issues.
As a key structure in the Arpan Draw watershed, Mary Stock is a focal point for water resource and climate enthusiasts interested in the intersection of water management, infrastructure sustainability, and environmental conservation. With its historical significance and current condition, this dam represents both a challenge and an opportunity for stakeholders to work together to ensure its resilience and continued contribution to the local ecosystem.
Year Completed |
1970 |
Dam Length |
300 |
Dam Height |
38 |
River Or Stream |
ARPAN DRAW |
Primary Dam Type |
Earth |
Surface Area |
7 |
Hydraulic Height |
33 |
Nid Storage |
87 |
Structural Height |
38 |
Outlet Gates |
Uncontrolled - 1 |
Hazard Potential |
Low |
Foundations |
Soil |
Nid Height |
38 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Powder River At Arvada
|
156cfs |
Wild Horse Creek Near Arvada
|
0cfs |
Piney Creek At Kearny
|
113cfs |
Clear Creek Near Buffalo
|
12cfs |
Rock Creek Near Buffalo
|
70cfs |
Clear Creek Near Arvada
|
256cfs |
Dam Data Reference
Condition Assessment
SatisfactoryNo 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
HighDams 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.
Mary Stock