The Grand Canyon of the Yellowstone is the most breathtaking sight inside Yellowstone Park. Twenty miles long, the canyon is up to 4,000-feet wide and 1,200-feet deep in places. From several vantage points, you can view Lower Falls plunging steeply into the canyon 308 feet, or the Upper Falls tumbling 109 feet.
Mineral stains mark the locations of hot springs and steam vents in the canyon walls. For thousands of years, upwardly percolating fluids have altered the chemistry of the rocks, turning them yellow, red, white, and pink.
When the old geyser basin was active, the "cooking" of the rock caused chemical alterations in the canyon's iron compounds. The rocks are essentially rusting. The colors indicate the presence or absence of water in the individual iron compounds. Most of the yellows in the canyon are the result of iron present in the rock rather than sulfur, as many people think.
The 19th century painter Thomas Moran said, "its beautiful tints were beyond the reach of human art."