Photo taken from Crystal Forest, AZ view area. - In flooding, the trees were washed from where they grew and accumulated in sandy river channels, where they were buried by layers of gravely sand, rich in volcanic ash from volcanoes further to the west. The volcanic ash was the source of the silica that helped to permineralize the buried logs, replacing wood with silica, colored with oxides of iron and manganese. Petrified Forest National Park Scenic Route