Volcano Hazards Program YVO Yellowstone Yellowstone was 640,000 years ago USGS producing 2,500 times according to enough to fill the Grand Canyon USGS Yellowstone Volcano Observatory history of eruptions was 640,000 years ago according to Yellowstone Volcanic History https://volcanoes.usgs.gov/volcanoes/yel...ge_54.html Yellowstone https://volcanoes.usgs.gov/volcanoes/...