Bighorn Canyon National Recreation Area is a national recreation area established by an act of Congress on October 15, 1966, following the construction of the Yellowtail Dam by the Bureau of Reclamation. It straddles the border between Wyoming and Montana. The dam, named after the famous Crow leader Robert Yellowtail, harnesses the waters of the Bighorn River by turning that variable watercourse into Bighorn Lake. The lake extends 71 miles through Wyoming and Montana, 55 miles of which lie within the national recreation area. About one third of the park unit is located on the Crow Indian Reservation. Nearly one-quarter of the Pryor Mountains Wild Horse Range lies within the Bighorn Canyon National Recreation Area.