Geologists have classified the rock layers into various formations.
Many formations also have different parts, or members.
These layers entomb the landscapes and lifeforms of a younger planet Earth. In the hill to the left, thin beds of reddish-brown rock known as shale were formed from silt and clay that came to rest in the quiet waters of lagoons, mud flats, and coastal flood plains. This 225 million year old rock is the Moenkopi Formation. Geologist believe that the Moenkopi, more than 950 feet thick in places, was laid down in a moist, tropical climate. The gray band of rock just above the Moenkopi is a greenish-gray shale that was once volcanic ash.