Southern tip of the Lemhi Range, eastern Snake River Plain. showing the wall of the Blue Creek caldera

Southern tip of the Lemhi Range on the northeastern margin of the eastern Snake River Plain showing the caldera wall of the 6.27 million year old Blue Creek caldera, in the Heise volcanic field.  Also shown are other units from the Heise volcanic field including the Kilgore Tuff and the Blacktail Creek Tuff.  In the foreground is the much thicker sequence of Walcott Tuff that was deposited inside the caldera and contains tight folds that indicate it was deformed shortly after the rocks were erupted at a time when the rocks were very hot (>580 °C, or 1075 °F), probably at the time the Blue Creek caldera collapsed. USGS Photo by L. A. Morgan (August 2007).