No. 4, also known as the Allied No. 4 Tailings Pond, is a private-owned structure located in Sweetwater County, Wyoming. Built in 1973 by designer George C. Toland, this earth dam stands at a height of 25 feet and serves the primary purpose of debris control along the Allied Draw river. With a storage capacity of 1356 acre-feet and a surface area of 175 acres, No. 4 plays a crucial role in managing water resources in the area.

Despite being classified as having a low hazard potential and a fair condition assessment, No. 4 is regulated by the State of Wyoming and undergoes regular inspections, with the last one conducted in November 2019. The dam features an uncontrolled spillway with a width of 60 feet, ensuring proper water discharge during peak flow events. While the risk assessment for No. 4 is moderate, the structure meets state guidelines for emergency action plans and risk management measures.

For water resource and climate enthusiasts, No. 4 presents an intriguing case study of a privately-owned earth dam that plays a vital role in debris control and water management in the region. With its historical significance and ongoing regulatory oversight, this structure exemplifies the intersection of infrastructure, environmental stewardship, and risk management in the context of water resource management.