Yellowstone National Park was formed thousands of years ago when a huge volcanic eruption shot an amazing amount of ash up into the air that ended up covering all of the western United States. It also managed to leave a blanket of ash over most of the Midwest, northern Mexico and even some parts of the eastern Pacific. The eruption was so large that it can't even be compared to the eruption of Mt. St. Helens in 1980. This huge event happened approximately 640,000 years ago - it was just one of the natural processes that helped form Yellowstone National Park the way we know it today.
Today you can experience such geothermal spots as Old Faithful. These areas provide evidence of how Yellowstone is one of the world's largest active volcanoes. In the past, the park's unusual features confused the first settlers in the area, but now they simply make up some of the most amazing attractions in this national park.