Petrified Forest National Park (PEFO) near the southern margin of the Colorado Plateau in the Painted Desert area of east-central Arizona is an area of spectacular scenery formed primarily from the Chinle Formation about some 225 – 208 Ma during the late Triassic (Ash, 2006). The paleoenvironments represented by the Chinle consists of fluvially derived sediments. Its largely illitic clays, which swell when wet and shrink when drying. This causes surface movement and cracks, which discourages plant growth, and enhances rock exposure. The park is exposed to wind and water eroding the Chinle into badlands, buttes, mesas and rounded hills (Ash, 2006)

 The Chinle Formation is the most widely exposed terrestrial Late Triassic formation in the world (Ash, 2006)  Map of PEFO. It comprises multicolored bentonitic mudstone, siltstone, sandstone, conglomerate, and silty limestone. The Chinle Formation was deposited primarily in a back arc basin. During the Late Triassic, Northern Arizona was situated near the western margin of the pangean supercontinent in the tropics. (Martz and Parker, 2008). The Chinle formation is dominated by fluvial sediments deposited by an extensive river system by westward and northwestward flowing streams as well as in lakes (Ash, 2006).

The Chinle formation in PEFO is about 932 feet thick and a disconformity overlies the early – middle Triassic Moenkopi Formation (Martz and Parker, 2008). The Formation is especially susceptible to weathering due to lack of plants. This weathering exposes many fossils, especially plants and tetrapods.  The fossils in PEFO indicate this area was populated by a large variety of plants and animals during the Late Triassic. (Martz and Parker, 2008)  PEFO is of course best known for its fossilized flora. Trees were buried in river sediment containing volcanic ash. Silica was dissolved and carried into the logs and crystallized into the trees forming deposits of colorful wood. 

The petrified wood is concentrated at four discrete geographically isolated sites in the Park called “fossil forests.” Each has a distinct name based on the character of the wood.