The refuge for a historically significant herd of free-roaming Mustangs is close to what lake? 
Bighorn Canyon National Recreation Area:  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. Pryor Mountains Wild Horse Range: The Pryor Mountains Wild Horse Range is a refuge for a historically significant herd of free-roaming Mustangs, feral horses colloquially called "wild horses", located in the Pryor Mountains of Montana and Wyoming in the United States.
Bighorn Lake