Ashfall, the Nebraska waterhole

Twelve million years ago a supervolcano in what is now Idaho blanketed Nebraska in ash. Animals gathered at a waterhole and died of lung failure over days and weeks, the big ones last, and were buried where they fell. A student found a rhino skull weathering out of a bank in 1971. What has been uncovered since is a death assemblage of complete, articulated skeletons, rhinos, three-toed horses, camels, birds, with unborn young inside some and last meals still in their teeth. The dig is roofed over and you walk above palaeontologists working on it. PUBLIC state historical park.