Fossils

• William Clark notices an exposed fossil rib in an area later known as the Hell Creek Formation
  Hell Creek Formation
  The Hell Creek Formation is an intensely-studied division of Upper Cretaceous to lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana...
  
  on the south bank of the Yellowstone River. Although he mistakenly believed the rib belonged to a huge fish, paleontologists have determined that this event marks the first documented dinosaur fossil discovery in North America.