Green Hills in Washakie, Wyoming, is a local government-owned dam designed by John Donnell for irrigation purposes. Completed in 1971, this earth dam stands at 17 feet high and spans 588 feet in length, with a storage capacity of 115 acre-feet. The dam on the Runway Draw river provides water for irrigation and recreation, with a spillway width of 20 feet and a maximum discharge of 337 cubic feet per second. Despite its low hazard potential and fair condition assessment, the dam undergoes inspections every five years to ensure its safety and functionality.

Located in Manderson, Green Hills dam plays a crucial role in managing water resources in the area, covering a surface area of 10 acres and draining a 2.5-square-mile watershed. With its stone core and soil foundation, the dam is regulated by the State Engineer's Office in Wyoming and meets state permitting, inspection, and enforcement requirements. While the dam has a moderate risk assessment rating, there are no designated emergency action plans or inundation maps prepared at present, emphasizing the need for ongoing risk management measures and updates to ensure the safety of the surrounding community and environment.