Petrified Forest National Park
Information on this web site is compiled by Jackie Gering
Amber Petrified trunk with Badlands in the Background
Table of Contents
The Petrified Forest became a National Park on December 9, 1962
The Petrified Forest is located in Northeast Arizona, near the southern edge of the Colorado Plateaus, and is part of the Colorado Plateau Physiographic province. The park which consists of 93,533 acres, contains five forests: the Jasper Forest, the Crystal Forest, the Black Forest, the Rainbow Forest, and the Blue Mesa.
Northeast Arizona has a very dry, hot, desert-like climate. The average temperatures in the summer tend to be in the 90's, with highs in the low 100's. At night the temperature usually drops to be between 50 - 60 degrees. Average winter daytime temperatures vary from the 40s to 50s with nighttime lows in the 20s and teens. Temperatures do occasionally dip below 0 degrees, and the Northeast region of Arizona has been known to receive occasional snow. The annual rainfall averages about 9 to 10 inches with 40% occurring as thunderstorms in the late summer. High winds can occur at anytime in the year, and being a rather dry climate, humidity usually remains very low (Travel Basics, Facts).
HOW WAS THE PETRIFIED FOREST FORMED?`
The petrified wood found in the forest was formed about 225 million years ago, during the Triassic period. At this time it is estimated that the Colorado Plateau area of northeastern Arizona was located near the equator and was part of a "super-continent" called "Pangea." This tropical location provided a very moist environment abundant with a lush landscape full of coniferous trees, ferns, cycads, and giant horsetails, which provided food and shelter to many insects, reptiles, amphibians, and even dinosaurs!!!!! As time went by, various trees died and fell to the ground, or they were knocked down by the raging floods. While some decomposed, others were carried away by rising rivers and were deposited on flood planes, where they were covered by sediments of ash that were spewed from the volcanoes of the west. As water dissolved the layers of sediments, silica from the ash was carried through the logs and filled in or replaced the once living cells. "This process was often so exact that replacement left a fossil that shows every detail of the logs' original surfaces and, occasionally, the internal cell structures" (Trees to Stone). Over time, the silica solution crystallized into the mineral quartz. The rainbow of colors which varies from log to log was caused by impurities such as iron, manganese, copper, and lithium. To find out more information on which impurities or minerals cause certain colors click HERE.
Cartoon sequence of the geologic history of the area
Cartoon sequence of the petrifaction process
After the fallen trees were covered by sediments, the area went through a period of many changes as the plates slowly shifted into the positions they hold today. About 60 million years ago the area was uplifted as part of the Colorado Plateau. When one looks at the logs found in the Chinle formation, it looks as if the logs have been cut by a chain saw. This is not the case. After petrification, the logs are composed mostly of quartz. So they are hard and brittle and fracture easily under stress caused from earthquakes or the uplift of the plateaus. During the Pliocene period (about two to five million years ago), when the area was very swampy, a layer of basalt was created by a lava flow that was underwater, called pillow lavas. These pillow lavas formed a cap rock, or a resistant layer that protected the layers underneath (Kervin). Over time weathering and erosion occurred, which slowly removed the layers to currently expose the Chinle Formation. It is within this formation that the most petrified wood is found.
During the Triassic period, a forest covered the land from Texas into Utah, and many different organisms flourished in the tropical setting. The Araucarioxylon arizonicum, Woodworthia, and the Schilderia are three types of tree specimens that thrived during this time period but are all now extinct (Trees to Stone). As stated above, the area was abundant with ferns, cycads, giant horsetails, and large coniferous trees towering almost two hundred feet tall and nine feet in diameter. This lush landscape provided a home for many insects, reptiles, amphibians, and dinosaurs.
 |
The Placerias gigas was a large, bulky plant-eating reptile weighing up to two tons. It had strong toothless jaws and large tusks which may have been used to dig up roots and tubers for food. |
 |
The Smilosuchus gregorii lived a crocodile-like life in the rivers and lakes preying on fish and smaller animals. Bony plates protected the body and tail. Fossils indicate that some may have reached 30 feet in length. |
 |
Desmatosuchus haplocerus was a 16 foot long, plant eating reptile that sported a long, pig like snout and looked like an overgrown armadillo. A bony shell covered the long narrow body and large spikes on its sides were probably used for defense. |
 |
Chindesaurus bryansmalli was an early primitive dinosaur, approximately 8 to 12 feet long from head to tail, with sharp, sickle-shaped teeth indicating that its diet was carnivorous. It was most likely one of the fastest land-dwellers in the area, with a light build and exceptionally long hind legs. |
 |
Postosuchus kirkpatricki was a large land-dwelling predator. It moved in a dinosaur-like way with its legs tucked under its body not sprawled out to the side like most reptiles. It was about 13 feet long. |
 |
Coelophysis bauri was one of the earliest known carnivorous dinosaurs. It was only about 8 feet long. The long slender jaws were lined with sharp, flattened teeth. The animal proably walked on its hind legs and used its forelimbs to catch and hold prey. The large eye sockets suggest keen eyesight. |
**All information in this chart was taken from the Petrified Forest National Park Website- Reptiles and Dinosaurs.
For information on the modern animals that live in the Petrified Forest National Park check out these links:
Reptiles Mammals Ravens Amphibians
Gunnison Prairie Dog Pronghorn
| ARCHAIC
MAN 7500 BC to AD 1 |
PUEBLO
II AD 900 to AD 1100 |
| BASKET
MAKER II AD 1 to AD 500 (Flattop site) |
PUEBLO
III AD 1100 to AD 1250 (Agate House & Puerco Ruin) |
| BASKETMAKER
III AD 500 TO AD 800 (Twin Buttes Site) |
PUEBLO
IV AD 1250 to AD 1450 (Wallace Tank / Stone Axe) |
| PUEBLO
I AD 900 TO AD 1100 (SITE 236) |
NAVAJO AD 1450 to PRESENT |
The Archaic man was a nomadic dweller who lived his life in search of food. This hunter and gatherer followed the game herds and searched for wild seeds, berries, roots (Baeza). There are no permanent dwellings for researchers to study only scatter stones, and relics. Material possession was kept to a minimum for these people due to the fact that they were constantly on the move.
Hundreds of years later appeared a descendant of the Archaic man, the Basket Maker (Baeza). These people lived in pit houses, and get their name from the beautifully woven baskets and sandals they created. The basket maker created warm clothes out of animal skins, made tools and weapons out of bone, wood, and stone, and even crude, poorly fired pottery. The most important thing he did was learn to cultivate corn. "The oldest excavated village in Petrified Forest National Park is a Basket Maker II site on the Flattops, twin mesas over-looking the Little Colorado River Valley and the mountains to the south. The village consisted of twenty-five round-to-oval pit houses dug into the rock of the mesa. The builders lined subterranean walls with upright sandstone slabs and added upper walls and roofs of brush and mud. Slab-lined chambers were used for burials. Baskets were still woven, but pottery had generally replaced them for everyday use" (Baeza).
By the time of Basket Maker III, life was much more advanced. The pit houses were deeper, support beams were added to the roofs, and ventilation shafts were in use (Baeza). Archeologists have found a wide variety of tools which suggests an expanded diet. Bows and arrows were used to hunt and kill larger game. Corals and shells found in the pit houses lead one to believe that these people were active in trade with other peoples from the pacific ocean and gulf of California. These people became better farmers as they cultivated squash, beans, and corn, and also learned ways to combat drought and built wind breaks to keep the crops from drying out and protect them from sand blowing in the wind.
Between 850 AD and 900 AD, severe droughts forced the people to leave the land in search of a more moist climate. As the climate began to change, more rain fell, people slowly began to return to the area. These people are called the Pueblo. During the Pueblo II, houses consisted of rock and mud rectangular masonry built homes above ground, some with multi-stories. In addition to farming corn, beans, and squash, they now farmed cotton, and domesticated turkeys (Baeza).
Once again, a severe drought forced the people to leave the area in search of water. The Pueblos soon returned after the drought was ended. They continued with there way of life and continued to advance and flourish as a society. Unfortunately, the weather patterns changed again in the beginning of 1300. This time rainfall increased. In the fall and winter, hard, cold rains came and washed away the floodplain farms. Summers had little rainfall which made it impossible to farm. "Trading activity and religious, artistic, and social accomplishments declined before the ancient enemy, drought" (Baeza). It is believed that these ancient peoples packed up their belongings and walked across the high plain to the mesas in the north where permanent water sources were available, abandoning their Pueblos.
Links to other Web Sites
Petrified Forest National Park
BIBLIOGRAPHY
Harris, Ann G., Esther Tuttle, and Sherwood D. Tuttle.
1997. Geology of National Parks (5th ed.).
Kendall/Hunt Publishing Co., Iowa. p. 102-112.
ANKYLIOGRAPHY
(Anonymous). 08 April 2002. Travel Basics (http://www.nps.gov/pefo/pphtml/basics.html). National Park Service. (Actual visit: 19 April 2002).
(Anonymous). The Facts (http://www.outdoorplaces.com/Destination/USNP/AZPetFor/pfnp6.htm#Climate). OUTDOORPLACES.COM. (Actual visit: 19 April 2002).
(Anonymous). 11 December 2000. Trees to Stone (http://www.nps.gov/pefo/treestostone.htm). National Park Service. (Actual visit: 19 April 2002).
Miller, Alisa C. 22 November 1998. Cartoon Sequence of The Geologic History of The Area (http://www.geo.arizona.edu/geos256/azgeology/pwood/ghist1.html). The University of Arizona. (Actual visit: 21 April 2002).
Johnson, Marian. 24 November 1998. How Does Wood Become Petrified (http://www.geo.arizona.edu/geos256/azgeology/pwood/pet1.html). The University of Arizona. (Actual visit: 21 April 2002).
Kervin, Bob. 23 May 1999. Petrified Forest National Park (http://www.iup.edu/fieldtrip/petrified.html). Indiana University of Pennsylvania. (Actual visit: 1 May 2002).
(Anonymous). 23 February 2001. Triassic Reptiles and Dinosaurs (http://www.nps.gov/pefo/triassicreptilesamphibians.htm). National Park Service. (Actual visit: 19 April 2002).
Baeza, Jo. 1999. Prehistoric Man in the Petrified Forest (http://www.wmonline.com/attract/pforest/preman.htm). White Mountains Online. (Actual visit: 19 April 2002).
(Anonymous). 11 December 2000. Petrified Forest National Park (http://www.nps.gov/pefo/pefohome.htm). National Park Service. (Actual visit: 19 April 2002).
This website was last modified on April 24, 2002