Eventually, the log leaves the groundwater table and goes through a process of "dewatering" and recrystallizing, this time as solid quartz. This process takes much longer — tens of millions of years, according to the fossil record. But why do so many of the logs appear "cut"? It has to do with how they got to their present location, Parker says: "About 60 million years ago, forces of geology started the uplift of the Colorado Plateau.
This area went from deeply buried to being uncovered and raised more than 1 mile above sea level. As a high point, it is continuously eroding away, exposing old rocks and their fossils, such as the petrified logs from the Triassic. The park consists of two main sections, and recent legislation has authorized doubling the land area to , acres.
Located in the south are the major concentrations of the famous colorful petrified wood; in the north rise the colorful banded badlands of the Painted Desert. Giant fossilized logs, many of them fractured into cord-wood-size segments, lie scattered throughout, like headstones bearing a deceased's likeness. Much of the quartz that replaced the wood tissue million years ago is tinted in rainbow hues.
Many visitors cannot resist taking rocks, despite strict regulations and stiff fines against removing any material. To see if the petrified wood was actually disappearing at an alarming rate, resource managers established survey plots with a specific number of pieces of wood; some were nearly barren in less than a week. The problem is not new. Military survey parties passing through the region in the s filled their saddlebags with the petrified wood.
As word of these remarkable deposits spread, fossil logs were hauled off by the wagonload for tabletops, lamps, and mantels. In the s gem collectors began dynamiting logs searching for amethyst and quartz crystals.
To prevent further destruction of its unique bounty, the area was designated a national monument in and a national park more than a half century later. If you are traveling west on I, exit into park. When leaving the south end of park, the road joins US Follow US for 19 miles to Holbrook and back to I If you are traveling east on I, take the US exit in Holbrook.
The south entrance is 19 miles farther. After driving through the park, leave via I Airport: Flagstaff. There is also a small airport in Holbrook. Summer's dramatic thunderstorms enhance the beauty of the landscape. Fall, with its milder weather, also attracts many visitors.
Winter on the Colorado Plateau can be cold with brief snowstorms, but moderate afternoon temperatures are not uncommon. The area blooms colorfully in spring; winds can be high. Many of the features at Petrified Forest are on a scale best appreciated by leaving the car. There are fossil trees that are related to living gingkos, too. Geologically speaking, how old are these trees? Radioisotopic dates zircons tell us that the trees in the Black Forest were deposited about million years ago and those in the Blue, Jasper, Crystal, and Rainbow Forests were deposited around million years ago.
Do the rings we see in some of the petrified wood represent annual growth rings? As sub-tropical to tropical trees, they probably grew year-round. There would need to be a growing season versus a non-growing season to create annual growth rings. How tall were these trees? Two trees in the Long Logs area of the Rainbow Forest measure and feet long.
This indicates that some of the trees may have approached at least feet 61 m tall when alive. Is this the largest concentration of petrified wood in the nation?
In the world? This is considered one of the largest concentrations in the world, with other large ones found in North Dakota, Argentina, and Egypt. What mineral s replaced the wood? The mineral silica, from volcanic ash, in various stages of crystallization replaced most of the organic wood.
Minor minerals, such as iron, manganese, and carbon add the rainbow of colors. Where were the volcanoes that provided the ash and silica to petrify these logs? Geological reconstructions of the Triassic Period show that there were volcanic mountain chains to the west and south.
What do all the colors in the petrified wood represent? The various colors represent the trace minerals in the quartz. Iron and manganese account for much of the coloration, carbon also can add black, and—rarely, there is chromium that provides a true green. In some cases the wood has not been completely agatized. What happened to the roots, branches, bark, and cones from the trees?
Few examples have been found physically attached to the logs, usually limited to the root base. There are specimens of leaves, reproduction structures, twigs and branches found as fossils in the park.
There are also a couple of bark samples from the park. When a tree dies, the bark falls off quickly because it is only held on by a thin membrane called the cambium. Leaves, needles, and blades fall off as well. Roots, branches, and remaining bark are knocked off by transportation in waterways. Is petrified wood good for anything? It is used as a semi-precious gemstone in jewelry and as an ornamental stone in book ends, clocks, furniture, etc. Petrified wood is valuable scientifically as fossils from around the world.
Much of the petrified wood of the park preserves the original cellular structure of the wood allowing paleontologists to identify the wood type and to create climatic reconstructions for the Triassic Period.
How heavy is petrified wood?
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