Petrified Forest National Park

The park states the rule without room for interpretation: removing anything or digging up anything, even partially exposed, is strictly prohibited. Given that the ground is carpeted in gemlike fragments of 225-million-year-old wood, that rule is the only reason there is anything left to see.

What you are looking at are trees from the Late Triassic, fallen into rivers, buried in sediment loaded with volcanic ash, and replaced cell by cell with silica. They lie in the Chinle Formation, the same colourful sequence that gives the Painted Desert its name. Around 60 million years ago the Colorado Plateau began rising and erosion went to work; every rock layer that once sat above the Chinle has since been stripped away here, which is why the logs are at the surface at all.

The wood is not the whole story. The same beds have produced Late Triassic ferns, cycads and ginkgoes, along with giant crocodile-shaped reptiles called phytosaurs, large amphibians, and some of the earliest dinosaurs. Palaeontologists have been working the park since the early twentieth century.

The park covers about 346 square miles across Navajo and Apache counties in northeastern Arizona, averaging 5,400 feet, and roughly a third of it, 50,260 acres, is designated wilderness. Headquarters sits 26 miles east of Holbrook on Interstate 40, which runs through the park beside the BNSF railway, the Puerco River and old Route 66. It was made a national monument in 1906 and a national park in 1962.

People got here 13,000 years ago. Ancestral Pueblo farmers were growing corn in pit houses by 2,500 years ago, living in masonry pueblos with great kivas a thousand years ago, and by 1450 they had moved on to the Hopi Mesas and Zuni, where their descendants live now. The Park Service asks visitors to stay off the badlands as well: climbing them does damage that lasts.

Commercial petrified wood from private land outside the park is sold legally at the gates.