Cabeza Prieta National Wildlife Refuge is a vast protected desert in southwestern Arizona along the Mexico-United States border, covering 860,010 acres in the Yuma Desert and ranking as the third largest national wildlife refuge in the contiguous United States. Established in 1939 to protect desert bighorn sheep after a statewide conservation campaign, it later formally opened in 1941 and now supports hundreds of animal and plant species adapted to severe desert conditions. Much of it was preserved as wilderness in 1990. Its isolation, limited access, active border crossing corridor, humanitarian controversies, and damage from border wall construction have made it a place where conservation, migration, and border politics sharply intersect.