The
Bruneau-Jarbidge caldera (sometimes called a
supervolcano) is located in present-day southwest Idaho. The
volcano erupted during the
Miocene, between ten and twelve million years ago, spreading a thick blanket of ash in the
Bruneau-Jarbidge event and forming a
caldera. 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 up to two meters of ash was deposited. At the time, the caldera was above the
Yellowstone hotspot.