This high, dry tableland was once a vast floodplain crossed by many streams. Tall, stately pine-like trees grew along the headwaters. Crocodile-like reptiles, giant fish eating amphibians, and small dinosaurs lived among a variety of ferns, cycads, and other plants and animals that are known only as fossils today. The tall trees - Araucarioxylon, Woodworthia, and Schilderia - fell and were washed by swollen streams into the floodplain. Silt, mud, and volcanic ash then covered the logs. This blanket of deposits cut off oxygen and slowed the logs' decay. Gradually, silica bearing groundwaters seeped through the logs and, bit by bit, replaced the original wood tissues with silica deposits. As the process continued, the silica crystallized into quartz, and the logs were preserved as petrified wood.
That was about 225 million years ago in the late Triassic Period. After that time, the area sank, flooded, and was covered with freshwater sediments. Later the area was lifted far above sea level and this uplift created stresses that cracked the giant logs. Over time, wind and water have worn away the layers of hardened sediments, exposing the fossilized remains of ancient plants and animals. The hills will continue to yield fossil treasures as ceaseless weather patterns sculpt the soft clay soils of the Painted Desert.
Today the ever present forces of wind and water continue to remove sediments. Erosion continues to break down the exposed logs and unearth the logs and other remaining fossils still buried below the surface. In some places, up to 300 feet of fossil bearing material remains. The petrified logs, other fossils of plants and creatures that lived in the area, and the rocks locking them in place all testify to changes in the environment through millions of years.
There are many stories here in the Petrified Forest. Evidence of early human occupation is readily visible on the landscape. Sites throughout the park tell of human history in the area for more than 10,000 years. We do not know the entire story, but there were separate occupations, a cultural transition from wandering families to settled agricultural villages, pueblos and trading ties with surrounding villages. Although evidence of these early people fades about 1400, their story remains through their dwellings, potsherds, and petroglyphs.
In the mid-1800s, U.S. Army mappers and surveyors exploring this area carried stories back East about the remarkable "Painted Desert and its trees turned to stone." Next, pioneers, ranchers, and sightseers made their way into the area. After a period of using the wood for souvenirs and numerous commercial ventures, territorial residents recognized that the supply of petrified wood was not endless. In 1906 selected "forests" were set aside as Petrified Forest National Monument. In 1932, 53,200 more acres of the Painted Desert were purchased and added.
In 1962 the area became Petrified Forest National Park, and in 1970, 50,000 acres within the park were further designated for preservation as wilderness. Research continues to unlock the geological and human stories set aside for present and future generations.