Volcanic Calderas

The sign counts two eruptions and stops. The first, about 2.1 million years ago, threw out some 2,450 cubic kilometres of rock and ash, the largest known in Yellowstone's history, and the ground fell into the Island Park Caldera, whose rim the sign claims for this pullout. The second, about 1.3 million years ago, blew out the smaller Henrys Fork Caldera at its western end. The third, about 640,000 years ago, made the caldera inside the park. The heat has stayed put while the continent drifts southwest over it, which is why the youngest caldera lies east.

What the plaque says

Volcanic Calderas Some 2,000,000 years ago, massive eruptions of hot rock boiled for 60 miles from this high rim on 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. 396 Text prepared by the Idaho Historical Society Marker made & installed by Idaho Transportation Department

Where it stands

Worth the stop nearby

• Mesa Falls — 5.4 mi
  The inn went up with a dam in mind. The dam never came, and the Henrys Fork still drops 114 feet untouched.
• Warm River — 7.7 mi
  Union Pacific built the Yellowstone Branch for tourists. At the bottom of this canyon it turned the engines that pushed them uphill.
• Harriman State Park — 11 mi
  The Harrimans would give Idaho their ranch only when Idaho had a parks department fit to run it. The state built one.
• Teton Dam Site — 20 mi
  Geologists warned that the canyon walls would leak. The warnings were softened, the dam was finished, and it never held a full reservoir.

More markers nearby

• The Three Tetons — 5.7 mi
• Caldera Lookout — 7.1 mi
• Harriman State Park — 8.7 mi
• Harriman Wildlife Refuge — 12 mi