Bison are the largest mammals at Yellowstone, some weighing almost 2,000 pounds. There are more than 4,000 of them in the park. The largest herd we saw was grazing near Old Faithful, where I made this iconic image. The massed bulk of these huge animals, aligned here shoulder to shoulder, is impressive enough. But to see them juxtaposed front and back against the steaming early winter landscape along the Firehole River, is to look back into American history itself. Bison have roamed the Yellowstone since prehistoric times, almost as long as the steam has poured from the land. To see these mighty forces of nature sharing the same frame is to see grandeur defined anew.