Some 2,000,000 years ago, massive eruptions of hot rock boiled for 60 miles from this high rim across Yellowstone Park. An exceptionally large crater remained when that lava surface collapsed. Another smaller caldera followed north of here about 1,300,000 years ago. Yellowstone's geysers and hot springs continue to spout as remnants of those volcanic displays formed as underground rock gradually moves westward across a tremendous source of interior heat.