Petrified Forest National Park is a United States national park in Navajo
and Apache counties in northeastern Arizona. Named for its large deposits
of petrified wood, the fee area of the park covers about 230 square miles,
encompassing semi-desert shrub steppe as well as highly eroded and colorful badlands.
During the Late Triassic, downed trees accumulating in river channels in what
became the park were buried periodically by sediment containing volcanic ash.
Groundwater dissolved silica (silicon dioxide) from the ash and carried it into
the logs, where it formed quartz crystals that gradually replaced the organic matter.
Traces of iron oxide and other substances combined with the silica to create varied
colors in the petrified wood.