Mainline 3, also known as Cemetery Canyon Dam, is a privately owned structure located in Crook, Oregon. Built in 1971, this earth dam stands at 42 feet high and spans 200 feet in length, with a storage capacity of 350 acre-feet for irrigation purposes on Cemetery Creek. The dam's maximum discharge rate is 67 cubic feet per second, with a significant hazard potential due to its condition being not rated.

The dam is regulated by the Oregon Water Resources Department and undergoes regular inspections, with the last one conducted in February 2020. Despite its age, Mainline 3 continues to serve its primary purpose of irrigation effectively, with a normal storage capacity of 168 acre-feet and a surface area of 12 acres. The structure is equipped with a slide gate outlet for water release, ensuring controlled management of water levels in the reservoir. Overall, Mainline 3 plays a vital role in supporting agricultural activities in the region and highlights the importance of proper dam maintenance and monitoring in the face of changing climate conditions.