Skip back in time 200 to 250 million years ago- North America is completely different. The Arizona, New Mexico, Utah, and Colorado (Four Corners) area was much closer to the equator (much like Panama today). Thick deposits of mudstones and sandstones were deposited in the region in low-lying, humid environments. If you fast-forward back to modern time, millions of years of wind and water have slowly ground down through these rocks to create many breathtaking areas (think: Canyon de Chelly, Petrified Forest). These rocks are not only geologically interesting, but they are also visually interesting. Below is one of the mudstone deposits (which is actually purple) from the Blue Mesa member of the Chinle Formation. This entire area is littered with ancient, fossilized tree trunks.
Eroded Mudstone, Petrified Forest National Park, AZ (16″x45″)