The petrified wood of the Petrified Forestis the 'State Fossil' of Arizona. The pieces of permineralized wood are fossil Araucariaceae, a family of trees that is extinct in the Northern Hemisphere but survives in isolated stands in the Southern Hemisphere. During the Upper (Late) Triassic this desert region was moist and mild. The trees washed from where they grew in seasonal flooding and accumulated on sandy delta mudflats, where they were buried by silt and periodically by layers of volcanic ash, derived from volcanoes further to the west. The volcanic ash was the source of the silica that helped to permineralize the buried logs, replacing wood with silica, colored with oxides of iron and manganese.
The Petrified Forest (1936) is a film, a gangster thriller starring Bette Davis, which uses the Petrified Forest area as an atmospheric isolated setting.