This was the first of many canyons we were to enjoy. The canyon was cut by the Yellowstone River and is subject to continuing hot spring activity. The entire park is in a huge volcanic crator formed over 625 million years ago and is still very active with thermal activity. The canyon varies in depth from 800 to 1200 feet and from 1500 to 4000 feet wide. It is about 24 miles long. The colorations in the rock are caused by thermal activity. We ran out of adjectives early from awsome to magnificant. It is too big for the camera and my vocabulary is not extensive enough to describe it all.