Petrified Forest, Arizona State, USA
The Petrified Forest is located in the southwest of the United States, in the state of Arizona. There are about 200 million years, the area was covered by swamps and it was crossed by many rivers. Upstream of these rivers grew tall conifers. Many trees were uprooted by storms and then they were then covered with mud, sand and volcanic ashes containing much silica. Once trees are buried away from air and near absence of oxygen, the decomposition process has stopped. The silica in volcanic ash has gradually crept into the wood cells and massive tree trunks turned into stone blocks. During the various geological eras, after a lot of landslides and erosion of sedimentary layers, calcified and petrified tree trunks are brought to the surface. Different colors are due to the presence of iron, manganese and carbon.
Click on a thumbnail to enlarge the image.