Petrified Forest National Park
Petrified Forest National Park straddles the border between Navajo and Apache counties in the US state of Arizona. The park, covers about 146 square miles (380 km²), and rises from a low of 5,340 feet (1,630 m) along the Puerco River to a high of 6,230 feet (1,900 m) at Pilot Rock. It was declared a national monument in 1906 and a national park in 1962.
The Petrified Forest is known for its fossils, especially fallen trees, ancient conifers that lived in the Late Triassic about 225 million years ago. At this time the area was a low plain flanked by mountains, with a sea to the west. Streams flowing across the flood plain deposited sediments and inorganic matter including trees and other plants and animals that had fallen into the water. Later, ash and lava from nearby volcanos added to the sedimentary deposits. Gradually minerals carried by ground water leached into the wood and crystallized, replacing the organic matter. About 60 million years ago the Colorado plateau, of which the park is part, was pushed upwards by tectonic forces, exposing it to increased erosion. The upper layers of rock were removed, leaving behind the fossilized logs. Other plant fossils include ferns, cycads and ginkgoes. These soft forms remain chiefly as compression fossils which have been flattened by the weight of the sediments above. Among the animal fossils that have been found are giant reptiles called phytosaurs, large amphibians and early dinosaurs.
In the north of the park is the Painted Desert, an area of soft sedimentary rocks containing abundant iron and manganese, which give the rocks their colourful, painted appearance. Here the climate is very dry, and this, along with the easily erodible nature of the rocks, means vegetation is almost non-existent, giving rise to the term Badlands.
Although the park is known primarily for its fossil logs and the Badlands of the Painted Desert, the main environment is semi-desert shrub steppe with swathes of open grassland and areas of shrubs, small trees, grasses and herbs, with larger willows and cottonwoods along the river banks. Some of the animals that inhabit this country are pronghorns, prairie dogs, coyotes and foxes. The pronghorn is the fastest land animal in North America and is capable of speeds up to 60 miles per hour (97 km/h).
Human habitation of the area started about 8,000 years ago. By about 2,000 years ago people were growing corn and soon after building pit houses. Later inhabitants built above-ground dwellings called pueblos. But by about 1,400 AD the climate had changed sufficiently for the area to be abandoned. Left behind were several archaeological sites including rock carvings.