Thousands of pieces of petrified wood are scattered across the Arizona desert like glittering jewels. Those perfect replicas of real trees have been left on hill slopes or ridges. Once they were all living trees, now the petrified forest: petrified forest.
Discovery by Lorenzo Sitgreaves
While driving through the dusty plains of Arizona’s Painted Desert in 1851, US Army officer Lorenzo Sitgreaves stumbled upon the remains of a very strange forest. Although it looked like a living forest, it was not made of trees with leaves or branches, but of rock-hard blocks of quartz crystal. That discovery raised two important questions: First, “What were these hard stumps doing in the middle of a dry desert, where no tree could stand in the scorching heat?” And secondly, “how had bark, sap, and softwood turned into these peculiar cold blocks of stone?”
History of the forest of stone
Two hundred million years ago, when the Arizona Desert was still a vast lowland, tall conifers grew on that great swampy plain, which was lined by a number of active volcanoes. Instead of today’s coyotes, lynxes, and badgers, dinosaurs roamed the huge coniferous trees on the hills to the south and on the flanks of volcanoes at the edge of the swampy basin. Most of those trees were about 30 meters high, with trunks nearly 2 meters in diameter. A single specimen was twice as thick. During flooding, many dead trees (lying on the ground) were carried away by the water. But some were left in river beds or in narrow gullies. The trees were covered with thick layers of silt, sand and volcanic ash. Silica from the ashes (dissolved in ground water) penetrated the wood and crystallized. The trunks became buried with more sediment. After thousands of years of elevation and erosion, the petrified forest came to the surface.
The crystallization process
The crystallization process has resulted in an infinite variation in color. Isolated silica molecules crystallize into pure quartz and many strains consist of this. If other minerals are present, all kinds of semi-precious stones are formed (such as amethyst, agate, jasper, onyx and carnelian). The cross-sections of the petrified tree trunks show that the features of the original wood have been well preserved in those petrified trunks. Silicic acid entered every cell and crystallized. The annual rings (which are now made of quartz) chart the entire life cycle of the tree. From the moment it took root to the moment it fell. In the case of the petrified forest, the silica crystals have always assumed the shape of the original tree cells, so that over time perfect copies of the trunks, sometimes up to 300 meters deep, were formed.
The Earth Forces
The petrified forest might never have surfaced if the Earth’s crust hadn’t risen about 65 million years ago. The forces that created the Rocky Mountains also propelled this part of Arizona. This had two important consequences. First, the area dewatered and the crystallized remnants of the coniferous forest were pushed up, and second, wind and rain eroded over time the layers of sediment, shale and sandstone covering the trunks and exposed the petrified forest.
Navajo and Paiute Indians
Before the arrival of the railroad in the 19th century, Indian tribes, including the Navajos and Paiutes, lived in the area of the petrified forest. Drawings carved into the sandstone walls are all that remains of Puerco, a place inhabited from AD 500 to 1400. When the petrified forest surfaced, the local people (the Navajo Indians) saw in the striped, shiny logs the bones of a legendary giant, the giant Yietso. The Paiute Indians, on the other hand, believed they were arrow shafts of Shinauv, the thunder god. In reality, however, they are the stone trees of the largest petrified forest in the world. The result of the natural process shown above.
Five trunk concentrations
There are five major tree trunks in the forest, named after the color of the predominant constituent in the usually opaque trunks. They are: Blue Mesa, Crystal Forest, Rainbouw Forest, Black Forest and Jasper Forest.
Blue Mesa
This is one of the most beautiful areas of the petrified forest. Between the colorful layers of the flat hills and the rocky cones you can clearly distinguish the layers of the old swamp. The petrified stumps are just fragments of the tree trunks. Some of the trunks of the Petrified Forest measure between two and nearly four meters in diameter, but most of the trees disintegrated into smaller pieces before the fossilization process started or before they came to the surface.
Crystal Forest
At the end of the 19th century, many pieces of tree trunks from the Crystal Forest (where the quartz existed in its purest form) were removed and crushed to extract the gem-like quartz crystals. Partly for this reason, it was decided in 1906 to declare Petrified Forest a national monument. In 1962, 380 square kilometers of the forest became a national park.
Jasper Forest
Long Legs (part of Jasper Forest) is where most of the ‘real’ tribes are located.
Other wonders of the forest
Other wonders of the forest include the Agate Bridge, a piece of log turned into a stone bridge, and Agate House, an ancient agate log cabin. In an area where nature has so clearly ruled, these are some of the few man-made things.
Fossil plants and animals
The same process that buried and then uncovered the tribes has also resulted in many fossils of plants and animals from 200 million years ago in this area. In addition to the conifers, many cycads (palm-like plants with fern-like leaves) grew. There are also fossils of dinosaurs (such as the phytosaurus with its crocodile snout) and the main prey of this dinosaur, the fish-eating Metoposaurus as well as the armadillo-like Aetosaurus.
Supplement fossils from the Giant Reptile Age
This area only receives 23 cm of rain per year (mostly during short, heavy thunderstorms). Still, that is enough to sometimes flush out an inch of soil. For example, the tree trunks and fossil stock is constantly being replenished with new evidence from the time when the giant reptiles populated the earth.