Petrified Forest National Park - Natural Features & Ecosystems (U.S. National Park Service)

NPS Photo

The Chinle and Bidahochi Formations as seen from Nizhoni Point.

Petrified Forest National Park contains the petrified remains of 225 million year old trees from the Late Triassic. Surrounding the petrified wood are millions of years of deposition, uplift, and erosion, creating the Chinle Formation. This rock formation creates the red hues of the Painted Desert and the blue tones of the Blue Mesa region.

Petrified Forest is situated near the southern edge of the Colorado Plateau with elevations ranging from 5300 feet to 6235 feet. It was the uplift of the Colorado Plateau, starting about 60 million years ago, and the erosion that followed and continues today, which carved the present landscape.

Photo by Marge Post

Bentonite clay contracts into a crusty and cracked surface that some say resembles elephant skin.

The colorful mudstones and clays of the Painted Desert badlands are composed of bentonite, a product of altered volcanic ash. The clay minerals in the bentonite can absorb water to as much as seven times their dry volume. The expansion and contraction properties of the bentonite cause rapid erosion by preventing much vegetation from growing on the slopes of the hills.

Photo by Marge Post

Twisted sandstone formations are sculpted as erosion eats away at the caprock of this mesa.

Other prominent features created by erosion are mesas and buttes. Both have flat tops of more erosion-resistant sandstone over softer clays. Mesas are quite broad but not very tall, while buttes are taller and more narrow. In this picture sandstone caps the top of an eroding mesa. The sandstone is more erosion resistant than the claystone underneath. Eventually the harder rock will erode away, leaving the softer claystone underneath exposed to the elements. This will then become another rolling bentonite hill within the badland landscape.