Island Park Caldera , in the U.S. states of Idaho and Wyoming , is one of the world 's largest calderas , with approximate dimensions of 80 by 65 km . Its ashfall is the source of the Huckleberry Ridge Tuff that is found from southern California to the Mississippi River near St. Louis . This super-eruption of approximately occurred 2.1 Ma ( million years ago ) and produced 2,500 times as much ash as the 1980 eruption of Mount St. Helens . Island Park Caldera has the smaller and younger Henry 's Fork Caldera nested inside it
1980 eruption of Mount St. Helens
1980 eruption of Mount St. Helens
Island Park Caldera