Much of the park's petrified wood is from Araucarioxylon arizonicum, an extinct conifer tree, while some found in the northern part of the park is from Woodworthia arizonica and Schilderia adamanica trees. At least nine species of fossil trees from the park have been identified; all are extinct. The park has many other kinds of fossils besides trees. The Chinle, considered to be one of the richest Late Triassic fossil-plant deposits in the world, contains more than 200 fossil plant taxa.

'Chinle' means "flowing through." The Navajo Tribe uses this word to describe soils washed down from Arizona's fertile highlands into its otherwise arid canyons and valleys. It also describes the sediment and organic materials that flowed into Pangaea's floodplains, including the remains of animals, trees, and other plants. Overtime, the accumulation of these deposits compressed into sedimentary rock that makes up the Chinle Formation of eastern Arizona's Petrified Forest National Park.