Brian and I descended back to ~7,000 feet for dinner in a small-town Indian restaurant in Nederland, Colorado, west of Boulder. By then, both our heads ached like a bad hangover, and my lungs literally burned when I tried to inhale anything but shallow breaths. Add generalized joint pain, and I had a full-blown case of altitude sickness. Given that I am a noted hypochondriac, I expected the worst.
The Pierre Shale formation was deposited during the Paleogene and Cretaceous periods about 70 million years ago. The region was covered by a deep sea—the Cretaceous Western Interior Seaway—which deposited massive amounts of shale on the seabed. Both the thick stratum of shale and embedded marine life fossils—including ammonites and skeletons of fish and such marine reptiles as mosasaurs, plesiosaurs, and extinct species of sea turtles, along with rare dinosaur and bird remains—were created during this time period. The area now known as Colorado was eventually transformed from being at the bottom of an ocean to dry land again, giving yield to another fossiliferous rock layer known as the Denver Formation.[58]
