Petrified Forest
About 200 to 250 million years ago the Colorado Plateau
area of northeastern Arizona was located near the equator
and on the southwestern edge of the largest landmass on the earth's surface.
Eventually this super-continent called "Pangea" seperated
to create our present continents.
Fossil evidence of this ancient land lies in the sediments called
the Chinle Formation which is now exposed in
Petrified Forest National Park.
Over time trees died.
Rivers carried the trees to the lowlands.
Some trees were deposited on the flood plain
adjacent to the rivers and others were burried in the stream channels.
A few trees were petrified, becoming the fossilized logs we see today.
Most of the fossilized logs are Araucarioxylon.
Small quantities of Woodworthia and Schilderia
are in the northern part of the park.
All three are now extinct.
Logs were buried in the sediment and covered with ash from volcanoes.
Ground water dissolved silica from the volcanic ash and carried it through the logs.
This solution replaced cell walls, crystallizing
as mineral quartz during the petrification process.
About 60 million years ago the region was uplifted
as part of the Colorado Plateau.
The Chinle Formation was exposed by erosion.
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