The high, dry, tableland of Petrified Forest National Park was once a vast floodplain. 225 million years ago, during the Triassic period, large, pine-like trees fell and were washed by swollen streams into this plain where the trees were covered with silt, mud, and volcanic ash. This blanket of deposits cut off oxygen and slowed the decay of the logs. Gradually, silica-bearing ground waters seeped through the logs, and bit-by-bit, encased the original wood tissues with silica deposits. As the process continued, the silica crystallized into quartz, and the logs were preserved as petrified wood.

The floodplain eventually sank, was flooded, and covered with freshwater sediments. Later, the area was lifted far above sea level. This uplift created stresses that cracked the giant logs hidden underneath. In recent geologic times, wind and water wore away the accumulated layers of hardened sediments. Today, many petrified logs, as well as fossilized dinosaurs, reptiles, fish, and plants, remain exposed on the land’s surface. Wind and water continue to remove sediments, and erosion continues to uncover other remaining logs and fossils still buried below the surface. In some places up to 300 feet of fossil-bearing material remains.

The petrified logs, fossils, and the rocks locking them in place all testify to changes in the environment that occurred through millions of years. There are other stories in the area, as well. Sites throughout the park tell of human history in the area for more than 2,000 years. Archaeologists don’t know the entire story, but they do know that there were separate occupations, a cultural transition from wandering families to settled agricultural villages, and trading ties with neighboring villages. This story of early people, told by potsherds, rubble, and pictures on the rocks, fades about 1400 A.D.

In the mid-1800s U.S. Army mappers and surveyors arrived in the area and carried home stories of the remarkable “Painted Desert and its trees turned to stone.” Next, farmers, ranchers, and sightseers made their ways into the area. After a period of collecting the wood for souvenirs and numerous commercial ventures, territorial residents recognized that the supply of petrified wood was not endless and that it needed to be protected. Selected “forests” were set aside in 1906 as Petrified Forest National Monument. In 1932 some 2,500 acres more of the Painted Desert were purchase and added to the monument. In 1962, the area became Petrified Forest National Park, and in 1970, 50,000 acres were further set aside as wilderness.

Source

• http://www.npca.org/parks/petrified-forest-national-park.html