The spectacular canyon that falls in a V-shape down to the Yellowstone river's tumultuous waters is called Grand Canyon of Yellowstone. The feature, which is about 20 miles long and ranges from between 800-1,200 feet deep, was formed only between 10,000-14,000 years ago, making it a very young canyon (compare that to the Grand Canyon in Arizona which has been in the process of being carved by erosion starting about 70 million years ago). Though, as the National Parks Service notes, exactly how the canyon was formed isn't well known as it hasn't been studied much. What makes this canyon so striking in part is the colors of the rocks lining the walls. The colors are actually from the iron found in the rocks, and different amounts of water affecting the different iron compounds. Essentially, the walls of the canyon are rusting. Even the yellows are due to this iron oxidation and not, as many think, to sulfur. If you'd like to see the canyon for yourself, there are many options for vistas along the North Rim Trail, including great opportunities to enjoy the Yellowstone river and its falls.