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The Petrified Forest National Park, Arizona, not only contains a mass of petrified wood but also the incredible Painted Desert, so called because of the multi-coloured rocks and sand. The area was discovered by US Army mapmakers in the mid-1800s and in 1906 was designated as a National Monument. The trees here were preserved by being covered with silt, mud and volcanic ash which cut off the oxygen and prevented serious decay. Silica-bearing ground waters gradually seeped into the logs and the silica crystallised into quartz, producing petrified wood about 225 million years ago. Later further geological changes revealed the forest to us. |
 Above: Huge logs of petrified wood lie all around the park. |
 | Left: The exposed face of the logs display a variety of coloured quartz. |
| Right: Although many of the tree trunks look as though they have been sliced with a chain saw these curious straight fractures are in fact natural breakage of the rock. |  |
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