Des Plaines crater:
- http://www.unb.ca/passc/ImpactDatabase/images/des-plaines.htm
- http://bulletin.geoscienceworld.org/cgi/content/abstract/73/8/959
- http://en.wikipedia.org/wiki/Des_Plaines_crater
- http://www.isgs.uiuc.edu/maps-data-pub/cook-atlas/fault.shtml
The short version is that 280 million years ago, an asteroid decided that it didn’t like Bill Roper’s music and decided to nail what is now Des Plaines, Illinois. Unfortunately for the asteroid, Roper wouldn’t be born for a number of years, so by the time he showed up, there was a 25 square mile crater, buried under quite a bit of glacial residue, and it looked in the geologic maps as it someone had taken a BIG hammer and smashed it down hard, once. All sorts of broken-up base rock.
See also Bill Higgins’ 2006 treatment of this.