225 million years ago, and in the Late Triassic geologic period, northeastern Arizona was part of the southwestern edge of the earth’s largest existing landmass, Pangaea and located near the equator. The area was a massive wetland region and covered with plant groups including lycopods, ferns, cycads, conifers and ginkgoes. As time elapsed, large forests were rapidly covered with sediment and became part of the geologic Chinle Formation which is located throughout the park.
Many of these fossilized logs are from a tree called Araucarioxylon arizonicum. Two others, Woodworthia arizonica and Schilderia adamanica, occur in small quantities in the northern part of the park. At least nine species of fossil trees have been identified from the Park. All of these trees are now extinct.