The only national park in the U.S. to contain a portion of the famous and historic Route 66 is Petrified Forest National Park.

National Park: 1962
Area: 146,930 acres (59,460 ha)
Address: 1 Park Road, PO Box 2217 
Petrified Forest, AZ 86028
Phone: (928) 524-6228Petrified Forest National Park is located in the greater Painted Desert—they are not two separate parks. While the Painted Desert encompasses about 1500 square miles, the park is about 150,000 acres—and not desert! Actually the main environment is short-grass prairie or intermountain-basin, semi-arid grassland. It is dry here, but there is snow in the winter and rain during the monsoon.

Geologic Formations

Erosion has sculpted and shaped intriguing landforms. The rocks reveal an enthralling chronicle of time that is unfolding and ever-changing. What can the rocks tell us? Think of the colorful layers as pages in a massive book.The first chapter of this geological text is the Chinle Formation.

Chinle Formation

The Chinle Formation was deposited over 200 million years ago during the Late Triassic Period. The colorful badland hills, flat-topped mesas, and sculptured buttes of the Painted Desert are primarily made up of the Chinle Formation, mainly fluvial (river related) deposits.

Within Petrified Forest National Park, the Chinle Formation is further divided to include the Blue Mesa Member, the Sonsela Member, the Petrified Forest Member, and the Owl Rock Member.

The Mesa Redondo Member is the oldest member of the Chinle Formation exposed in the Petrified Forest, mainly in the Tepees area. The Mesa Redondo consists of dark red siltstones as well as sandy conglomerates.

The top of the member is very colorful hard layer with yellow, red, and purple mottles. The Mesa Redondo was deposited between 225-227 Million years ago and represents floodplain deposits that were adjacent to the sandstone channels of the Shinarump Member.

The Blue Mesa Member consists of thick deposits of grey, blue, purple, and green mudstones and minor sandstone beds, the most prominent of which is the Newspaper Rock Sandstone. This unit is best exposed in the Tepees area of the park. The Blue Mesa Member is approximately 220-225 million years old.

The Sonsela Member is divided into three parts:

1) the upper Flattops One Bed, which consists of a thick cliff-forming brown, cross-bedded sandstone,

2) the middle Jim Camp Wash Beds of blue, grey, and purple mudstones and numerous small grey and white sandstone beds, and

3) the lower Rainbow Forest bed consisting of white cross-bedded sandstone and conglomerate of rounded pebbles and cobbles which contains the logs of the Rainbow Forest. This sandstone caps Blue Mesa, Agate Mesa, and the mesa north of the Rainbow Forest. The Sonsela Member is approximately 216 million years old.

The Petrified Forest Member consists of thick sequences of reddish mudstones and brown sandstone layers. This member is exposed in the Flattops and is the white and pink reworked volcaniclastic unit of the Painted Desert.

It contains large amounts of petrified wood. The Black Forest Bed, part of the Petrified Forest Member north of Kachina Point, has been dated isotopically at 213 +/- 1.7 million years old.

The Owl Rock Member consists of pinkish-orange mudstones mixed with hard, thin layers of limestone. Lenses of selenite gypsum are scattered periodically throughout the Owl Rock Member representing the minerals left behind after evaporation of inland lakes. This member is exposed on Chinde Mesa at the northernmost border of the park. The Owl Rock Member is approximately 205 million years old.

The colorful layers in the Chinle Formation represent ancient soil horizons. The coloration is due to the presence of various minerals. While the red and green layers generally contain the same amount of iron and manganese, differences in color depend on the position of the groundwater table when the ancient soils were formed.

In soils where the water table was high, a reducing environment existed due to a lack of oxygen in the sediments, giving the iron minerals in the soil a greenish or bluish hue. The reddish soils were formed where the water table fluctuated, allowing the iron minerals to oxidize (rust).

Bidahochi Formation

During the Late Miocene and Early Pliocene Epochs of the Neogene Period (4-8 million years ago) a large lake basin with ephemeral lakes covered much of Northeastern Arizona. Fine-grained fluvial and lacustrine (lake related) sediment such as silt, clay, and sand represent the lower part of the Bidahochi Formation.

Volcanoes, both nearby and as far as the Southwestern Nevada Volcanic field, spewed ash and lava over the land and into the basin. Many of the volcanoes were phreatomagmatic, when ground or lake-water mingled with eruptive material (magma) to cause explosive eruptions. The resulting ash formed fine-grained deposits that were deposited within the lake sediments.

After a few million years of erosion, most of the Bidahochi Formation has been removed from the park area, leaving volcanic scoria cones and maars (flat-bottom, roughly circular volcanic craters of explosive origin).

The vent from one of these maars is exposed on the Painted Desert Rim across the park road to the east of Pintado Point. The Hopi Butte Volcanic Field, which can be seen from the northern overlooks of the park extending northwest, is considered one of the largest concentrations of maar landforms in the world, covering about 965 square miles (2,500 square km).

The erosion-resistant lava flows, such as Pilot Rock and the Hopi Buttes, protect the softer lake-bed deposits beneath.

Where the Bidahochi and Chinle Formations make contact is an unconformity. An unconformity represents missing rock layers which in turn represents missing time. It’s like a geology textbook with missing pages.

You can tell that a page is missing but you can’t tell what was on them. The Chinle Formation was deposited over 200 million years ago but the Bidahochi Formation is only about 8 million years ago.

The contact between the Bidahochi and Chinle Formations represents 192 million years of missing time!

Pleistocene and Holocene Sediments

Pleistocene and Holocene Epoch (1.8 million years ago to present) deposits of windblown sand and alluvium (deposited by flowing water), now cover much of the older formations of the park.

At higher elevations in the northern part of the park, 500,000-year-old dunes can be found. Younger dunes, around 10,000 years old, are found in drainage areas that contain sand such as Lithodendron Wash.

The youngest dunes are found throughout the park, in all settings, deposited around a thousand years ago. These dune deposits are largely stabilized by vegetation, especially grasses.

While not as numerous as the fossils of the Chinle Formation, fossils have been found even in the quaternary sediments, including fragments of an ancestral proboscidean (elephants and their relatives, such as mammoths).

The Little Colorado River and its tributaries, including the Puerco River, have cut their own valleys into the soft Chinle and Bidahochi Formations of the Painted Desert.

Plants & Ecosystem

 

The natural world of Petrified Forest is far more complex than it seems on the surface. Located near the southern edge of the Colorado Plateau, the park is part of an amazing geological region. 

Petrified Forest has two geological formations, the Late Triassic Chinle Formation and the Mio-Pliocene Bidahochi Formation. Ancient environments are represented by these layers. 

The colorful Painted Desert badlands are composed of bentonite, a product of altered volcanic ash. The clay minerals in the bentonite can absorb water and swell much as eight times their dry volume. The expansion and contraction properties of the bentonite cause rapid erosion including by preventing much vegetation from growing on—and thus fixing—the slopes of the hills.

Mesas and buttes are other features created by erosion. The flat tops are created by the presence of cap rocks, more erosion-resistant rock such as sandstone over softer clays.

The softer rock is protected by the cap stones, but, as the sides weather and the protective rock falls down, the softer rock erodes away as it is exposed to the elements.

Without the capstone, the feature becomes another rolling badland. Mesas typically are wider than they are tall while buttes are taller than they are wide. Towers, monuments, and hoodoos are even further eroded features.

The types of plants and animals found in the park depend on the elevation, minerals in the soil and rock, and availability of moisture. Within the park, you may see open grassland, shrublands, little juniper-cliffrose woodlands, riparian and spring habitats. 

Grasses are one of the most important plants within the grassland ecosystem found in the park. Large expanses of grasslands form where wind-blown sediment and erosion have created a layer of soil several feet thick.

One of the most devastating causes of grassland destruction is grazing by livestock. Because grazing has not been allowed within the park for over fifty years, the area has returned to a more natural state and is one of the largest recovering grasslands in the Southwest.

In many areas of Petrified Forest National Park, large collections of exposed rock surfaces are covered by lichens. A lichen is a simple community of at least two mutually-dependent organisms: fungi and green algae. 

Green algae uses the photosynthesis process to produce food for the fungus, while the fungus protects the algae from the elements and extracts nutrients from soil and rock. The lichen structure is more elaborate and durable than either fungus or algae alone. 

Many other plants benefit from the presence of lichens. The green algae component of lichens can transform nitrogen in the air, which is unusable to most organisms, into a form which is essential for life. This is especially important in arid climates where lack of nitrogen is known to limit productivity.

Lichens are well adapted to arid climates. They can absorb more than their own weight of water and can absorb ephemeral water, such as dew, almost directly into their cells. The water does not need to go through roots and stems as it does in vascular plants.

Wildlife

Animal life at Petrified Forest includes amphibians, birds, insects, spiders, mammals, and reptiles. Birds, lizards and rabbits are seen most frequently, though seasons and weather play a large role in determining what animals are active.

For many animals, activity occurs during a particular temperature range. Crepuscular animals are active at dawn and dusk, the coolest times of day. The half-darkness makes prey animals less visible, yet visibility is good enough to locate food.

Activity can change with the season, too. Snakes and lizards are diurnal (active during the day) in late spring and early fall, but they become crepuscular during the heat of summer.<.p>

Many animals in the park are nocturnal (active at night). This is an adaptation not only to avoid high summer daytime temperatures, but also to avoid certain predators.

You are much more likely to see animal life in the park if you come as early as park hours allow and stay as late as allowed. These are also the times when the angle of the sun makes the views and colors of the Painted Desert most spectacular.

Whenever you are in a national park, do not approach, feed, or harass any wildlife. Help your parks reduce the impact of human visitors to the homeland of many wild species.

Petrified Forest has a variety of habitats. Raptors, songbirds, and ground birds can be found in the grassland. Riparian corridors provide food and shelter for warblers, vireos, avocets, killdeer, and others.

The exotic and native trees and shrubs around the Visitor Center and Rainbow Forest Museum provide home for western tanagers, hermit warblers, and house finches. The park also offers sightings of vagrant shore birds and rare Eastern birds not seen often in Arizona.

Rarities, such as black-throated blue warbler, have been found by Maricopa Audubon Society members. September and early October seem to be the best time to visit the area to see these fascinating vagrants.

Well-adapted to the often dry environment of Petrified Forest National Park, reptiles play an important part in maintaining the health of the ecosystem. Over sixteen varieties of lizards and snakes make Petrified Forest their home.

Reptiles occupy a variety of habitats ranging from grassland to rocky slopes. They consume large quantities of insects, spiders, scorpions, other reptiles and small mammals thereby preventing infestations of any single species. Respecting the entire reptile community helps to preserve this vital link.

When lizards are seen scurrying across a rock or path, please resist the urge to catch them. Lizards can have a mean bite and some will actually shed a tail to escape capture. Though the tail will grow back, a great deal of body energy is used in the process and population dynamics will be affected. Enjoy them from a respectful distance.

It is hard to imagine that in this dry region animals requiring consistent moisture could thrive. Three hundred and fifty million years ago the first fish-like amphibian hauled itself out of the sea.

Fossilized remains of giant amphibians, such as metoposaurs, have been discovered within the sedimentary rock of the park. By the time dinosaurs appeared, amphibians were flourishing. While much smaller, we still have amphibians in the park today, primarily several varieties of salemanders and toads.

Mammals are a diverse group of animals, ranging from the delicate white-footed mouse to the elegant mule deer. Mammals have fur or hair, produce milk for their offspring, and are warm-blooded.

In the often extreme climate of the plateau country, animals use such survival strategies as hiding in their burrows or migration as well as physiological adaptations, like hollow hairs for insulation or radiation of heat from body parts.

Many animals in arid regions are nocturnal or crepuscular, using the cooler night to survive the heat of summer or the darkness of the late hours to escape notice of predators.

Early morning and dusk are the best times to view mammals while in the park. Do not approach, feed, or harass any wildlife in Petrified Forest or any other national park area.

Some of the many species of mammals found in the park:
Coyote, Canis latrans
Gray fox, Urocyon cinereoargenteus
Swift fox, Vulpes velox
Bobcat, Lynx rufus (Felis rufus)
Mule deer, Odocoileus hemionus
Pronghorn, Antilocapra americana
Ringtail, Bassariscus astutus
Raccoon, Procyon lotor
Badger, Taxidea taxus
Striped skunk, Mephitis mephitis
Western spotted skunk, Spilogale gracilis
Black-tailed jackrabbit, Lepus californicus
Desert cottontail, Sylvilagus audubonii
Desert shrew, Notiosorex crawfordi
Pallid bat, Antrozous pallidus
Townsend’s big-eared bat, Corynorhinus townsendii (Plecotus townsendii)
California myotis, Myotis californicus
Fringed myotis, Myotis thysanodes
Yuma myotis, Myotis yumanensis
Canyon bat Parastrellus Hesperus (formally known as western pipistrelle, Pipistrellus hesperus)
Porcupine, Erethizon dorsatum
Gunnison’s prairie dog, Cynomys gunnisoni
White-tailed antelope squirrel, Ammospermophilus leucurus
Spotted ground squirrel, Spermophilus spilosoma
Rock squirrel, Spermophilus variegatus
Botta’s pocket gopher, Thomomys bottae
White-throated woodrat, Neotoma albigula
Bushy-tailed woodrat, Neotoma cinerea
Mexican woodrat, Neotoma mexicana
Stephens’ woodrat, Neotoma stephensi
Ord’s kangaroo rat, Dipodomys ordii
Silky pocket mouse, Perognathus flavus
Northern grasshopper mouse, Onychomys leucogaster
Brush mouse, Peromyscus boylii
Canyon mouse, Peromyscus crinitis
White-footed mouse, Peromyscus leucopus
Deer mouse, Peromyscus maniculatus
Pinon mouse, Peromyscus truei
Western harvest mouse, Reithrodontomys megalotis
House mouse, Mus musculus

History & Culture

More than 13,000 years of human history and culture are represented at Petrified Forest National Park. People first came to the area in nomadic groups following the last Ice Age, and have been present ever since.

Paleoindian
13,500 to 6,000 BCE 

At the end of the last Ice Age, the Southwest region was very different than today: higher rainfall, cooler average temperatures, green grasslands, wooded river bottoms.

Paleoindians were highly mobile groups who gathered food and hunted large animals like mammoth and bison. They found the Petrified Forest area a highly attractive, resource-rich setting.

Paleoindian groups are known for their large, well-made projectile points used for hunting game. At Petrified Forest, the people used petrified wood to create a range of different types of stone tools.

Early Paleoindian groups, with their distinctive elegant fluting of projectile points, help define the Clovis and Folsom Cultures of these ancient people. Folsom, Clovis, and later Paleoindian camps have been found within Petrified Forest National Park.

Archaic
6,000 to 500 BCE

The post-Ice Age climate became warmer and dryer, causing megafauna like the mammoth to go extinct. People had to broaden their food sources to include many different species of plants and animals.

Though still mobile, they decreased how far they moved around the landscape. The decreased mobility and wider range of food sources set the stage for domesticating plants and animals.

At the end of the period, corn was introduced from further south, starting a dramatic change in how people lived. Artifacts of this period are more diverse, including stone tools as well as one-handed manos and basin metates used to grind maize.

Basketmaker
500 BCE to 650 CE

By this period the park’s climate had become similar to what we experience today. The Basketmaker people built more permanent villages consisting of slab-lined pit houses.

They focused on farming, growing corn, squash, and eventually beans. But the remains of small game (such as rabbits) show further diversity in their diet.

Sivu’ovi is the largest known Basketmaker II village in the park, consisting of at least 47 pit houses and numerous storage pits. It is currently thought that Sivu’ovi was occupied seasonally, when the surrounding lands could be farmed.

Artifacts found there include Adamana Brown-style pottery, some of the earliest ceramics in northern Arizona.

Pueblo I
650 to 950 CE

The transition into Pueblo Periods shows that people were becoming even more fixed to one place on the landscape. People began to build more substantial above-ground structures, moving out of their pit houses and into the clusters of stone structures we call pueblos.

The use of ceramics for cooking and storage was very important. Today, these are the most common artifacts found at Pueblo sites. Ceramics changed from plain brown and gray vessels to corrugated varieties for cooking and storage, and more decorative types with intricate black-on-white designs.

Pueblo II-III
950 to 1300 CE

The Pueblo II and III periods span momentous times in the Southwest. The settlement at Chaco Canyon ushered a sphere of influence that spanned the Four Corners region, marked by increased village sizes, new architecture, and introduction of ceremonial kivas.

Ceramics during this period show increased diversity of designs, going from corrugated and black-on-white pottery to black-on-red and polychrome pottery as well. At Petrified Forest, the use of petrified wood as a building material became popular, creating the “agate houses” throughout the park.

Pueblo IV
1300 to 1540 CE

The Petrified Forest lies at the crossroads of major migration and trade routes along the Little Colorado and Puerco Rivers. This leads to an unparalleled diversity of ceramic types dating to this period. Types have been traced to groups hundreds of miles away throughout Arizona, New Mexico, and Utah.

Puerco Pueblo, founded during the Late Pueblo III period, is a fine example of a large village of its time. Consisting of over 100 rooms located on the banks of the Puerco River, it probably had a population of around 200 people. The inhabitants farmed along the flood plain and traded with their neighbors up and down the river. Puerco Pueblo and the Petrified Forest area were largely depopulated in the early 1400s due to a long standing drought that affected the agricultural-based settlements. The park was never fully abandoned, but there was a large movement of people to nearby larger population centers (Zuni and Hopi, for example).

The end of this period in the Southwest coincides with the arrival of Spanish explorer Francisco Vazquez de Coronado. His was the first European expedition to see the Grand Canyon and Colorado River.