The eastern Snake River Plain is a topographic depression that cuts across Basin and Range Mountain structures, more or less parallel to North American Plate motion.Beneath more recent basalts are rhyolite lavas and ignimbrites that erupted as the lithosphere passed over the hotspot.Younger volcanoes that erupted after passing over the hotspot covered the plain with young basalt lava flows in places, including Craters of the Moon National Monument and Preserve.[4] The northwest Nevada calderas have diameters ranging from 15 to 26 km and deposited high temperature rhyolite ignimbrites over approximately 5000 km2.Animals were suffocated and burned in pyroclastic flows within a hundred miles of the event, and died of slow suffocation and starvation much farther away, notably at Ashfall Fossil Beds, located 1000 miles downwind in northeastern Nebraska, where a foot of ash was deposited.By its characteristic chemical fingerprint and the distinctive size and shape of its crystals and glass shards, the volcano stands out among dozens of prominent ashfall horizons laid down in the Cretaceous, Paleogene, and Neogene periods of central North America.The Henry's Fork Caldera in Idaho was formed in an eruption of more than 280 km3 (67 cu mi) 1.3 million years ago, and is the source of the Mesa Falls Tuff.If Heise is any indication, this could mean that the Yellowstone Caldera has entered its final stage, but the volcano might still exit with a climactic fourth caldera event analogous to the fourth and final caldera-forming eruption of Heise (the Kilgore Tuff) – which was also made up of so-called "light" magmas.