The Petrified Forest National Park in Arizona

In northeastern Arizona lies a region named El Desierto Pintado or The Painted Desert by Spanish explorers. In its midst is a 346 square region that is the Petrified Forest National Park. Part of the late Triassic Chinle Formation (which is formed of mudstone, siltstone, sandstone, and conglomerate deposited into channels and floodplains of a large river system) the park is part of a broader area famous for petrified fallen trees from forests that date to the Late Triassic Epoch, about 225 million years ago. Pushed upwards starting around 60 million years ago the upper layers were eroded away by wind and rain exposing fossils. A humans in the area only began about 8000 years ago, when migrants entered the region eventually growing corn, and building pit houses and pueblos. Changing climate conditions eventually drove the descendants of these settlers out of the area and into the Hopi and Navajo regions.

Early Tourist Guide for the Petrified National Forest

Ever since the early 20th century, scientists have been unearthing and examining the rich fossils deposit in the Painted Forest. Giant reptiles called phytosaurs, large amphibians, and others have been discovered here, but the most famous fossils are those of plants of the Late Triassic Mesozoic period including ferns, lycophytes, cycads, gingkoes and others. At the time these plants and creatures lived, the park was part of the super-continent Pangaea, and located much further south, near the equator in fact, and the climate of the region was humid and sub-tropical, far different from the barren and arid deserts of today.

A view at Petrified Forest National Park, a site managed by the National Park Service in Arizona.

_{By AndrewKPepper – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=83635779}

The most famous of plant fossils and the namesake of the park is petrified wood. These fossils were created when downed trees accumulated in river channels flooded by tropical rainstorms became buried by sediment containing volcanic ash from nearby volcanic that erupted periodically. The quick burial of these plants in an ash mineral rich, low oxygen environment proved ideal for fossilization as low oxygen inhibits the decay of organic matter and deters the presence of many hungry critters (from bacteria on up). Over time silica (silicon dioxide) from the ash dissolved into the water began to form quartz crystals (also a form of silicon dioxide) on edge of the logs eventually replacing the organic matter as it slowly decayed. Iron oxide and other substances in the ash created different colors in quartz minerals creating over a very long period of time beautiful, (sometime brilliantly) colorful plant fossils. There are rare specimens of green petrified wood fossils that also stand out, the green coming from chromium. These tree fossils are sometimes monumental in size, feet in diameter and sometimes the length of (broken) tree logs.

Detail of colorful petrified wood, Petrified Forest National Park, Arizona, USA

_{By Brian W. Schaller – Own work, FAL, https://commons.wikimedia.org/w/index.php?curid=29628344}

Green Petrified Wood from Holbrook, Navajo County, Arizona, USA Size: 3.8 x 2.1 x 1.6 cm. The bark on both sides is very well preserved. This is a polished slice from petrified tree limb

_{By Rob Lavinsky, iRocks.com – CC-BY-SA-3.0, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=10175980}

Green Petrified Wood fromSize: 4.0 x 2.0 x 1.5 cm. The bark on both sides is very well preserved. You can see the distinct knots, where smaller limbs were once attached and the corrugated nature of the bark.

_{By Rob Lavinsky, iRocks.com – CC-BY-SA-3.0, CC BY-SA 3.0,} https://commons.wikimedia.org/w/index.php?curid=10176074

This fossilization process typically preserves details of the external shape and structure of the woody material including sometimes the bark, but in a small number of specimens the fossilization process penetrated into and preserved the cellular structure of the plant or animal bone. Paleologists and Paleobotanists can sometimes study these special fossils under a microscope to understand their cellular structure and this has brought a wealth of knowledge about species with no known relatives alive on the surface of the earth today.

At least nine species of extinct tree have been identified among the park’s fossils some growing up to 9 feet in diameter and up to 200 feet high. Perhaps the most famous of all is a conifer tree named Araucarioxylon arizonicum that grew from the Early Permian period through the Late Triassic. It’s closest living relatives are the Monkey Puzzle Tree and the the Norfolk Island Pine tree both of which only live in the southern hemisphere.

Artistic reconstruction of the plant Araucarioxylon arizonicum according to the descriptions given for the species from its Triassic fossil remains. The maximum height estimated for the species is 60 meters and its diameter is 60 centimeters. The columnar trunk with monopodic branching is observed and the lateral branches grow at an angle of 90º with respect to the axis and present negative geotropism. The structure of the leaves is unknown.

_{By Falconaumanni – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=37304138}

Fossil Araucarioxylon arizonicum (petrified wood) outside the National Museum of Natural History, USA, in Washington, DC, USA.

_{By Daderot – Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=27276482}

There are other fossils as well, preserved through what is known as compression fossilization, which been preserved by being flattened by the weight of sediment accumulated above it until only a thin film of fossil remains. These types of fossils have preserved leaves, seeds, pine-cone, spore, fish, insects, pollen grains and sometimes animal remains.

Recently scientists in the park retrieved a quarter mile deep core sample to understand the history of the earth better. One of the questions they trying to answer is whether three the impact of at least three mountain sized asteroids created a tectonic movement leading to the eruption of chains of volcanoes could have been the key cataclysmic event that ripped apart Pangaea – the earth’s single supercontinent at the time. It turns out the core provides evidence of two different potential story arcs: the change in the fossil record at the time could be connected to powerful asteroid impact in Canada which left behind a 62 mile wide impact crater, or that no single catastrophic event was responsible for the.

Incidentally, Petrified wood is not limited to Arizona. It occurs anywhere the conditions are right. For example, we’ve previously written about the petrified forest in the protected national monument on the Greek Island of Nesbos. Namibia too, has an exceptional petrified forest national park. Discovered by a pair of farmers in the 1950s, the enormous fossilized tree trunks in this case did not originate in the area where they were found, but instead were washed downstream of a river by a great flood. These trees date back to about 280 million years ago.

Typical Veld Landscape near Petrified forest in Namibia

_{By Olga Ernst – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=72029500}

Petrified Wood in Namibia

_{By t_y_l – P9133880, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=76429571}

Petrified Wood in Namibia

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Closeup view of Namibian Petrified Wood

_{By Lidine Mia – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=99649068}

Petrified wood is found all around the region in Arizona including outside the Petrified Wood National Park, but don’t forget when visiting the park itself that it is both illegal and unethical to take fossils from public land! Do the right thing and enjoy the fossils in their natural place in the park and go home with beautiful memories and photographs.

Originally built with agatized wood blocks and mud mortar, Agate House likely housed a single family sometime between 1050 and 1300, during the Late Pueblo II – Pueblo III Periods. The scarcity of artifacts suggests a relatively brief occupation. Due to its relatively large size, Agate House may have served as a central gathering place. Indeed, Agate House was a part of a much larger community. When first recorded by archeologists in the 1930s, the petrified wood construction of Agate House was thought to be unique. Since then, hundreds of similar petrified wood structure sites have been found in the park, indicating a history of humanity as colorful and diverse as the building blocks of Agate House. Agate House @ Petrified Forest National Park, Arizona

_{By daveynin – https://www.flickr.com/photos/44124370018@N01/49518910517/, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=88114729}

We have our own petrified forest of sorts at Georarities! Visit our Petrified Wood category to find samples of Arizona, Indonesian, green chromium petrified wood, and other varieties that you can buy for your collection!