Petrified Forest National Park
Location: Navajo County, Arizona
Time: 230 to 220 million years ago, during the Triassic period
About this Famous Find: Petrified Forest National Park is located in northeastern Arizona on the southern end of the Colorado Plateau. The reddish-brown and tan siltstones, sandstones, and conglomerates have yielded abundant remains of plants and animals from the Triassic. During this time, North America was located near the equator, on the southwestern edge of the supercontinent Pangea. This tropical latitude resulted in a relatively humid climate, marked by monsoonal weather patterns and distinct wet/dry seasons. In northeastern Arizona, braided rivers, streams, and ponds dominated the landscape and by the end of the Triassic, a large lake covered much of the region.
A lush landscape developed in this tropical climate. Ferns, cycads, giant horsetails, and coniferous trees (up to three meters in diameter and 70 meters tall) grew abundantly. Some of these large trees were buried where they stood by floodplain deposits, or were washed downstream and buried in river channels. Eventually these tree stumps and logs became fossilized as mineral-laden waters percolated through the sediments. Years of uplift and erosion since the Triassic have exposed these logs for us to see.
In the lush forests, a great diversity of insects, archosaurs, dicynodonts, and at least three species of dinosaur thrived. The environment also supported an abundance of aquatic animals, including molluscs, crustaceans, fish, crocodilomorphs, amphibians, and phytosaurs.
The fossilized wood was first recognized in this region by Native Americans. Over-collecting of fossils by geological expeditions in the 1850s threatened the area until Lester Ward from the U.S. Geological Survey proposed to protect the site in 1899. By 1906, at the request of local citizens, the Petrified Forest was named a National Monument and, along with the Painted Desert, it was designated a National Park in 1962. In addition to the park itself, collections from this area are housed at the American Museum of Natural History and the University of California Museum of Paleontology.