Yellowstone is the only place in the United States where bison have lived continuously since prehistoric times. A number of Native American tribes especially revere Yellowstone’s bison as pure descendants of the vast herds that once roamed the grasslands of the United States. The largest bison population in the country on public land resides in Yellowstone. It is one of the few herds free of cattle genes. Yellowstone is the only place in the United States where bison have lived continuously since prehistoric times. We know they lived here in centuries past due to fossils, oral histories from Indian tribes, and the stories of the earliest travelers to this region. Yellowstone bison historically occupied approximately 7,720 square miles (20,000 sq km) in the headwaters of the Yellowstone and Madison rivers. Today, this range is restricted to primarily Yellowstone National Park and some adjacent areas of Montana.