A 470-million-year-old impact structure under the town, unconfirmed and unseen
A meteor about 200 metres across came down on the eastern edge of what is now Decorah, in the Middle Ordovician, roughly 470 million years ago. The structure it left is a POSSIBLE impact crater rather than a confirmed one, and it is worth saying so: this is read from what lies under the town, not from a rim you can walk. Iowa looks like the least dramatic ground in America until you find out what is beneath it.
Other places on the map within a couple of hours of here.
