The Grand Canyon of the Yellowstone ranges from 800 to 1200 feet in depth and from 1500 to 4000 feet in width, with a length of about 24 miles. Its upper 2½ miles is the most colorful section. Through the ages, hot spring activity has altered the lava rock to produce lovely colors that are largely due to varied iron compounds, and steam vents and geysers are still at work on the canyon walls.