The Yellowstone hot spot, a 16 million-year old volcanic system covering southeastern Oregon, southern Idaho, southwestern Montana, and northwestern Wyoming is one of Earth’s largest silica-rich volcanic systems.
In northwestern Wyoming the Yellowstone volcanic system, is a large, Pleistocene, silicic volcanic field that is distinguished by three large calderas. There have been three major eruptions at Yellowstone in the past 2.1 million years. The last major eruption occurred 640,000 years ago and formed the Yellowstone caldera. Since that time there have been approximately 80 smaller eruptions, such as lava flows. The youngest of these ranges from 70,000 to 160,000 years old.