Fossil logs are embedded in the Chinle Formation (-225 million years ago) and the younger Morrison formation (-160 million years ago). Petrified wood began its evolutionary journey when floods and erosion uprooted trees and deposited them in flood plains. Trees were buried quickly and did not oxidize and decay. Ground water rich in silica dioxide and other chemicals saturated the buried trees. Minerals displaced the cellulose in the trees and caused the beautiful colors seen in petrified wood.
