Bison

If any animal would symbolize the American West as well as Yellowstone National Park itself, it would be the bison. Hunted to near extinction, they have made a remarkable comeback here. At the park's founding they numbered just a few more than 20 animals. There are now around 25oo in the park.
When the calves are born in the spring they have that interesting orange color. Within a few months, however, they have that more familiar brown color that they will keep for the rest of their lives. Unlike the elk, bison have a very strong instinct to protect the herd members. When one is hurt or attacked the rest will gather for protection.

Ahh. There's nothing like a good scratch. That photo is from Laurie Lyman.