Huckleberry Ridge Tuff is a vast volcanic deposit in Wyoming and Idaho formed by the Huckleberry Ridge eruption in the Yellowstone hotspot system about 2.1 million years ago. That eruption, tied to the creation of the Island Park Caldera, ranks among the largest known in Yellowstone’s history, producing about 2,450 cubic kilometers of ash and debris that later hardened into tuff. Researchers believe it likely unfolded in three phases separated by decades. As the third most recent of Yellowstone’s major caldera-forming eruptions, it was followed by the events that produced the Mesa Falls Tuff and Lava Creek Tuff. It remains an important record of ancient Yellowstone volcanism and caldera formation.