The desert is composed of stratified layers of
siltstone,
mudstone, and
shale of the
Triassic Chinle Formation, which erode easily. These fine-grained rock layers contain abundant iron and manganese compounds, which provide the pigments for the various colors of the region. Thin, resistant
lacustrine limestone layers and
volcanic flows cap the
mesas. Numerous layers of
silicic volcanic ash occur in the Chinle and provide the silica for the
petrified logs of the area. The erosion of these layers has resulted in the formation of the
badlands topography of the region. In the southern portions of the desert, the remains of a Triassic period
coniferous forest have
fossilized over millions of years. Wind, water and soil
erosion continue to change the face of the landscape by shifting
sediment and exposing layers of the Chinle Formation. An assortment of fossilized
prehistoric plants and animals are found in the region, as well as ancient
dinosaur tracks and evidence of early human habitation. ==Area and climate==