Photographs of Mesa Falls ash-flow tuff, Yellowstone National Park

Mesa Falls ash-flow tuff, Yellowstone National Park, Wyoming
 Mesa Falls ash-flow tuff and underlying fallout ash exposed in a quarry near Ashton, Idaho. This area was near the depositional margin of the ash flows and consequently the ash-flow tuff is nonwelded and contained abundant large pumice blocks. The tuff was deposited during a large eruption that produced the Henrys Fork caldera southwest of Yellowstone National Park 1.2 million years ago. Photograph by Dan Dzurisin.
Mesa Falls ash-flow tuff, Yellowstone National Park, Wyoming
 Closer view of Mesa Falls ash-flow tuff and underlying fallout ash exposed in a quarry near Ashton, Idaho. Photograph by Robert L. Christiansen in July 1983.