The Yellowstone region has produced three exceedingly large volcanic eruptions in the past 2.1 million years. The first of these caldera-forming eruptions, 2.1 million years ago, created a widespread volcanic deposit known as the Huckleberry Ridge Tuff, an outcrop of which can be viewed at Golden Gate, south of Mammoth Hot Springs. This titanic event was one of the five largest individual volcanic eruptions known anywhere on the Earth. A similar, smaller – but still huge – eruption occurred 1.3 million years ago. This eruption formed the Henrys Fork Caldera, located in the area of Island Park, west of Yellowstone National Park, and produced another widespread volcanic deposit called the Mesa Falls Tuff. The region’s most recent caldera-forming eruption – 640,000 years ago – created the 35-mile-wide, 50-mile-long (55 by 80 km) Yellowstone Caldera.
Source: Yellowstone Volcano Observatory