Sheldon National Wildlife Refuge spans 573,504 acres on Nevada’s northern border, extending slightly into Oregon across arid Great Basin volcanic terrain. Established by executive order in 1931, it was created to restore pronghorn habitat, protect native fish, wildlife, and plants, and provide sanctuary for migratory birds; most of its present land was added in 1936 as the Charles Sheldon Antelope Range. Advocates value it as one of the few largely intact sagebrush steppe ecosystems in the Great Basin. It supports pronghorn, sage-grouse, bighorn sheep, migratory birds, and the narrowly distributed Alvord chub, while also reflecting long-standing opal mining and the contested removal of free-roaming horses by 2014.