In the center of Yellowstone is the caldera, the crater left by the volcano some 600 centuries ago. The Hayden Valley is in the northeast corner of the caldera and is home to many of the 5000 bison in the park. One picture below is of a herd of bison crossing a creek in the valley with hot springs in the distance. Many trees in the park have bark rubbed off from the bears and deer. Mammoth Hot Springs, on the north edge of the park is a collection of hot springs that have moved the limestone into constantly changing shapes of travertine. Also, the area here, just north of the Teton range, is mountainous. As the snow on the peaks melts, there is a lot of water coming down in creeks and rivers dropping in elevation fast enough to form rapids and water falls all thru the park.