Petrified Forest National Park

The Petrified Forest National Park lies in the arid northeast of Arizona in the Painted Desert (so called because of its brilliantly colored sandstone in shades of red and blue).

Origins

In the Mesozoic era this was a plain traversed by numerous watercourses, with a vegetation of horsetails, ferns and coniferous trees in particularly well watered areas. When a tree fell it was covered by river-borne sediments and sealed off from the air, hindering the natural process of decay. In wet periods water containing silicon oxides filtered into the rotten wood, and when it became drier the water evaporated and the silicon oxides crystallized. The concentration gradually became so high that quartz (rock crystal, amethyst, agate, onyx, cornelian, jasper, etc.) was formed, preserving the internal cell structure and the external appearance of the trunk. Then in geologically recent times erosion by wind and weather freed the petrified plant remains from the overlying sandstone and brought to light not only fossilized plant remains (fern leaves, pine cones, etc.) but fossils of shellfish, snails, fish, amphibians and reptiles.