Fortunately, this monument is easily accessible since it is crossed by two main highways, thus giving visitors to northern Arizona an excellent opportunity to enjoy the beauties of this unusual work of nature. The National Park Service of the United States Department of the Interior has been entrusted with the responsibility of protecting and administering this and all of the other national monuments and parks forming America’s National Park System. It is the responsibility of all the people, as owners of these outstanding national values, to help the Service keep the wonders of this and other parks and monuments intact for the enjoyment of future generations. Because of the name “Petrified Forest,” many people who have read of it expect to find trees “turned to stone” and standing upright just as they grew. Actually, geologists who have studied the area very carefully do not believe that many of the living trees grew in this particular location, for all of the evidence indicates that fallen timber from forests a considerable distance away was carried here by flood waters of ancient streams and stranded and buried in the mud and shallows of lagoons and marshes. During the latter part of what geologists call the Triassic period, about 160 to 170 million years ago, most of northeastern Arizona was apparently an extensive flood plain; low, flat, and swampy. Numerous streams, some of them quite large, flowed out from the surrounding low hills into the plain. These streams brought enormous quantities of sediments; mud, sand, and other minerals, spreading it out layer upon layer as they shifted their flow back and forth just as on present river deltas. These sediments contained huge amounts of volcanic ash which the streams apparently picked up near their sources. This ash was largely silica, the mineral which was later to be of major importance in the petrification of the wood. (Silica (SiO₂) is the oxide of silicon, a non-metallic element making up 28 per cent of the earth’s crust. The crystal form of silica is quartz, the commonest of all minerals, which is found in large amounts in many volcanic rocks.) The flood plain was broken by an occasional ridge or high spot, apparently tree-covered, as a few petrified stumps with partial root systems have been found in the locations where they apparently grew. However, most of the trees grew in forests on the low hills through which these rivers flowed, anywhere from a few miles to 50 or 100 miles or more to the west and southwest of the present national monument. These trees died from various causes, just as trees of our modern times do. Fire, wind, insects, diseases, and other causes all took their toll. Many trees probably decayed in the forest where they fell, but others were picked up by flood waters and were eventually transported by the streams to the flood plain there to become stranded with hundreds of others and to be covered by the sediments brought in by the streams.