Huckleberry Ridge Tuff

The Huckleberry Ridge Tuff is a tuff formation created by the Huckleberry Ridge eruption that formed the Island Park Caldera that lies partially in Yellowstone Park, Wyoming and stretches westward into Idaho into a region known as Island Park. This eruption of 2,500 km³ of material is thought to be the largest known eruption in the Yellowstone Hotspot's history. This eruption, 2.1 million years ago, is the third most recent large caldera forming eruption from the Yellowstone hotspot. It was followed by the Mesa Falls Tuff and the Lava Creek Tuff eruptions.

...
Wikipedia