Petrified Forest National Park

Petrified Wood

This high, dry Arizona grassland was once a vast floodplain crossed by many streams. Tall, stately conifer trees grew along the banks. Crocodile-like reptiles, giant amphibians, and small dinosaurs lived among a variety of ferns, cycads, and other plants and animals known only as fossils today. The trees, Araucarioxylon, Woodworthia, Schilderia, and others, fell, and swollen streams washed them into adjacent floodplains, A mix of silt, mud, and volcanic ash buried the logs. This sediment cut off oxygen and slowed the logs’ decay. Silica-laden groundwater seeped through the logs and replaced the original wood tissues with silica deposits. Eventually the silica crystallized into quartz, the animals became fossils and the logs were preserved as petrified wood.

Stories abound in Arizona's Petrified Forest. Evidence of early human occupation is readily visible. Sites and fossils throughout the park tell of human history in the area for thousands of years. We do not know the entire story. But there were separate occupations, a cultural transition from wandering families to settled agricultural villages – or pueblos – and trading ties with surrounding villages. Although evidence of these early people in the park fades about 1400, their story is still told by their dwellings, pot sherds, and petroglyphs.

In the mid-1800s U.S. government mappers and surveyors exploring this area carried stories back East of the remarkable "Painted Desert and its trees turned to stone." Next, pioneers, ranchers, and sightseers made their way into the area. After a period of using the wood for souvenirs and many commercial ventures, territorial residents recognized that the supply of petrified wood was not endless. In 1906 President Roosevelt set aside selected stands of the petrified trees as Petrified Forest National Monument. In 1932 53,200 more acres of the Painted Desert were bought and added to the monument, and in 1962 Congress designated the monument as a national park. In 1970 Congress designated 50,000 acres in the park as one of the first National Park System wilderness areas. Research continues to unlock the wealth of geological, paleontological, and human stories set aside for present and future generations here. Today the story of your visit is added to the long history of Petrified Forest National Park.

Commercial Sources of Petrified Wood in Arizona

Petrified wood’s varied colors came from minerals in the silica-saturated waters. Iron, carbon, manganese, and sometimes cobalt and chromium produced patterns and blends of yellow, red, black, blue, brown, white, and pink. Petrified wood is surprisingly heavy, weighing nearly 200 pounds per cubic foot, and its hardness is seven on a 10-point scale.

It is illegal to collect or remove any petrified wood from the park. Samples of the same quality from the same deposits – but collected outside the park – may be obtained from nearby commercial sources. Petrified wood slabs are cut with giant, oil-cooled diamond saws. Then they are ground with silicon carbide grit to smooth the saw marks and roughness. This is followed by hours of polishing. Artisans fashion jewelry and other decorative objects from polished pieces.

Research into Fossils Continues

Paleontologists have studied fossils in the park since the 1920s. Their important finds include skeletons of crocodile-like phytosaurs; one of North America’s earliest dinosaur fossils, nicknamed "Gertie;" and most recently a skeleton of the aetosaur Stagonolepis, a large, heavily armored plant-eating reptile. Supported by donations, paleontogists still make fossil discoveries and try to figure out what this land was like.

Colors in The Tepees Area

Distinct white layers are sandstone. The cap of The Tepees is clay. Dark layers are caused by high carbon content. Darker reds are iron-stained siltstone. Reddish bases are stained by iron oxide, which is also called hematite.