Petrified Forest of Northern Arizona
August 30, 2013
Photographer: Nel Graham
Summary Author: Nel Graham
The Petrified Forest desert area in northern Arizona is perhaps the best example in the world of a fossil environment from the late Triassic Period (about 225 million years ago). Located on the southern edge of the Colorado Plateau, the forest is today primarily native grassland. Petrifaction of the trees likely occurred when they were washed into a floodplain and encased in silt and volcanic ash. Over the eons, cellulose was replaced by silica and minerals in the silt and ash deposits as they leached into the wood.
Other fossils that have been discovered here include large trees (mostly Araucarioxylon arizonicum), ferns, cycads, ginkgoes, phytosaurs, large amphibians, and early reptiles. They're all found in the Chinle Formation. Many of these fossils are weathering out of bentonite, a type of expanding, impure clay formed from volcanic ash. Photo taken in the summer of 2005.
Photo details: Camera Maker: OLYMPUS OPTICAL CO.,LTD; Camera Model: C3100Z,C3020Z; Focal Length: 6.6mm; Aperture: f/3.2; Exposure Time: 0.0013 s (1/800); ISO equiv: 100; Software: QuickTime 7.6.6.