This undated image supplied by the U.S. Fish and Wildlife Service shows bison at the Rocky Mountain Arsenal National Wildlife Refuge in Commerce City, Colo., with the Rocky Mountains in

 

              This undated image supplied by the U.S. Fish and Wildlife Service shows bison at the Rocky Mountain Arsenal National Wildlife Refuge in Commerce City, Colo., with the Rocky Mountains in
This undated image supplied by the U.S. Fish and Wildlife Service shows bison at the Rocky Mountain Arsenal National Wildlife Refuge in Commerce City, Colo., with the Rocky Mountains in the background. The park, which opens a nine-mile do-it-yourself Wildlife Drive Oct. 13, was built on a former Superfund site just outside of Denver. (AP Photo/Josh Barchers/DPRA)