of
Petrified Forest National Park
70 million years ago: Through tectonic movement of the earth's crust, Arizona and the rest of the continent began to move away from the equator and the other continents. This was also a period of mountain building, during which the Colorado Plateau began to isolate and uplift, causing stress to the fossils contained within the Chinle Formation.
5-16 million years ago: Near the end of the Cenozoic, during the Pliocene, a shallow lake as large as Lake Erie covered much of Northeastern Arizona. Deposits of silt and sand eventually formed sedimetary rock that can still be seen in the Painted Desert. Lava and ash from nearby volcanoes flowed down to and into the lake, eventually forming the dark cap rock found on Pilot Rock and the Rim of the Painted Desert. These deposits make up the Bidahochi Formation.
Pleistocene to the Present: Since the Ice Age, erosion has shaped the land of the Petrified Forest region. Today the activity continues, although the climate has become more arid, exposing the treasures within the layers of Petrified Fore
