Petrified forest is made up of tree trunks that were buried in mud, sand, or volcanic ash ages ago and have turned to stone. This action is caused by water that carries dissolved mineral matter. The water seeps through the mud and sand into the buried logs. There it fills the empty cells of the decaying wood with this matter until the structure has become solid stone. This stone shows many details of the original wood structure, especially under the microscope.
Petrified << PEHT ruh fyd >> logs are buried in various rock formations from different geologic periods. These fossils represent the types of trees that grew during a certain period. Petrified forests have been found in many states, especially in the Western states and New York.
In the United States, the most famous petrified forest lies in northern Arizona, near the town of Adamana. It covers about 40 square miles (100 square kilometers), which have been set aside as the Petrified Forest National Park. Thousands of petrified logs may be seen lying about on the surface where water has washed away the rock in which they were buried. On the average, the logs measure 3 to 4 feet (0.9 to 1.2 meters) across and 60 to 125 feet (18 to 38 meters) long. Most of them have broken into many pieces and lie scattered about. Only a few logs are still whole and none of them stand upright. The logs were carried there by a flooded river perhaps around 225 million years ago. As they traveled down the river, they were stripped of their branches and leaves. Through the ages, many of the logs have become rainbow-colored. Thousands of people have visited Petrified Forest National Park to see this scenic display. 
In life, the logs were the trunks of coniferous trees related to the Norfolk Island pine. Today they consist largely of quartz and opal, two forms of silica. Their yellow, red, purple, and black colorations were produced by impurities of the oxides of iron and manganese.
