Discovered a petrified forest that existed more than 225 million years ago at the end of the Triassic Period.
The geology of Petrified Forest National Park is similar to many other parks of the Colorado Plateau. Erosional landforms, sculpted from flat rocks characteristic of arid regions, dominate the scenery. But here, embedded in the Chinle Shale formation, thousands of petrified logs appear in an array that is unsurpassed for variety and profusion anywhere else in the world. This high, dry tableland surrounding Petrified Forest National Park was once a vast floodplain crossed by many streams. To the south, 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 Schilderiafell — were washed by swollen streams into the floodplain.
There they were covered by silt, mud and volcanic ash, and this blanket of deposits cut off oxygen and slowed the logs’ decay. Gradually silica-bearing ground waters seeped through the logs and, bit by bit, encased the original wood tissues with silica deposits. Slowly the process continued, the silica crystallized into the 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, was 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. Still later, in recent geological time, wind and water wore away the gradually accumulated layers of hardened sediments. Now the petrified logs and fossilized animal and plant remains are exposed on the land’s surface and the Painted Desert has its present sculpted form.
