Geology And Geophysics

Desert Geology the Painted Desert



Tweet
Thor's image for:
"Desert Geology the Painted Desert"
Caption: 
Location: 
Image by: 
©  

The Painted Desert of Arizona is a crescent shape arc starting from a bit north of Cameron. It then curves southeast beyond the Petrified Forest, with the Puerco and Little Colorado rivers bounding it in the west and south edges. To the northeast, it rises into the flat tables of Hopi Mesas and the Moenkopi Plateau.

It may seem that the boundary of the Painted Desert is clearly identified, but few people actually agree on where to place the exact boundaries of the desert. Some say it should be based on rainfall, others say it should be bounded in the valley of the Little Colorado from Holbrook to the Grand Canyon (Houk, 1991). However you define its boundaries, the fact remains that it is a spectacular location with breath taking scenery.
This report presents the Painted Desert's special features, as well as its geologic, palaeontological, and anthropological history. Some information about the Petrified Forest National Park will also be presented in these sections.

PAINTED DESERT

The Painted Desert is classified as a desert based on its annual rainfall, which is less than ten inches. Typical of a desert, it has few inhabiting animals, mostly rodents and small lizards, and vegetation so sparse that a solitary fragrant wildflower can take on the status of a landmark.
With an elevation of 4,500 feet, winter in the desert is as miserable as you could not want. Snow makes up most of the annual precipitation, and the land becomes featureless and bleak every winter.
The wind in the Painted Desert is usually harsh and constant with an average velocity of 30 mph. In 1975, the US Geological Survey started recording wind velocities, but their equipment became so clogged with sand that they had to abandon the project (Houk, 1990). The Desert Winds Project now uses satellites to record wind velocities. During a spring storm in 1981, wind speeds where recorded at a constant 40 mph with gusts up to 60 mph for six straight hours (Houk, 1990).
The beautiful colorations of the landscape change with the light. The best time to view the Painted Desert is at sunrise or sunset when the light completely brings out the hues for which the desert is known. It has been said that there are "168 distinct colors and shades in the sands of the Painted Desert, and to any beholder this seems conservative, rather that an exaggeration" (Houk, 1990).

The geology of Petrified Forest National Park and the Painted Desert is typical of the Colorado Plateau. Erosional landforms, sculpted from flat rocks characteristic of arid regions, dominate the scenery (Harris et al; 1997).
The landforms of the Painted Desert have been described as a multicolored layer cake. The variety of hues in the sandstone and mudstone layers of the Chinle Formation is the result of the varying mineral content in the sediments and the rate at which the sediments were laid down. When the sediments of the Chinle Formation were deposited slowly, oxides of iron and aluminum became concentrated in the soil. These concentrations create the red, orange, and pink colors seen at the north end of the park. During a rapid sediment buildup such as a flooding event, oxygen is removed from the soil forming the blue, gray, and lavender layers (Harris et al; 1997).



The following is a brief summary of the geologic history of the Painted Desert adapted from Harris et al; 1997:

1. Subsurface Paleozoic Rocks
No Paleozoic rock outcrops in park due to erosion
2. Moenkopi Formation: Early Triassic
Costal plain deposits 300-600 feet thick
Very little remains in the park due to erosion
Interfingered marine and continental deposits
3. Chinle Formation: Shinarump Member
Basal conglomerate deposited unconformably over the eroded Moenkopi Formation fining upward
4. Chinle Formation: Lower Petrified Forest
Shales and sandstones deposited in basin
5. Chinle Formation: Sonsela Sandstone
Contains most of the petrified wood of the park
Missing in some places in the park
6. Chinle Formation: Upper Petrified Forest
Shales and sandstones deposited in basin
Volcanic activity in the western sea: Ashfalls
7. Chinle Formation: Owl Rock
Gypsiferous clays deposited in lagoons
Volcanic activity in the western sea: Ashfalls
8. Burial (Throughout Chinle Formation deposition)
Trees uprooted during floods
Quickly covered: Prevented decay
9. Deposition of Jurassic and Cretaceous sediments
Several thousand feet deposited
Eroded away in the park
Helped to compact Chinle Formation while ground water permineralized the wood with silica
10. Tertiary uplift, warping, and erosion
Laramide Orogeny & Defiance uplift
Caused erosion of Jurassic, Cretaceous, and some of the Triassic beds
New mountains cut off moisture-laden winds from the Pacific
11. Bidahochi
Late Cenozoic sedimentation and volcanism
Basaltic debris from volcanic vents northwest of the Petrified Forest
12. Pleistocene and Holocene erosion
Glaciers caused pluvial climate - periods of high precipitation
Erosion slowed down with time as area became more arid



PALEONTOLOGY

This high, dry tableland surrounding Petrified Forest National Park was once a vast floodplain crossed by many streams. To the south, tall, stately pine-like trees grew along the headwaters. Crocodile-like reptiles, giant fish-eating amphibians and early dinosaurs lived among a variety of ferns, cycads, and other plants and animals.
The main species of trees that have been preserved in the park are Araucarioxylon, Woodworthia and Schilderiafell. They were washed downstream in the Late Triassic by floods and then covered by silt, mud and volcanic ash. The oxygen was cut off from these decaying logs, which prevented decay and allowed for replacement by silica from silica rich water that seeped through the logs and encased the original wood tissues creating the petrified wood that is found throughout the area today. After each rainfall, more fossilized material is exposed, and it is believed that there is about 300 feet of fossil bearing material left (NPS, Guides).

ANTHROPOLOGY

Painted Desert Inn

The Painted Desert Inn is on a mesa top overlooking the beautiful Painted Desert. It was built between 1937 and 1940 using portions of the walls left over from the Stone Tree House that was built in the early 1920's by Herbert Lore as a small rest house for travelers. The Inn has the style of Pueblo Revival, sometimes called Spanish/Pueblo style because of the Spanish Colonial elements included (NPS, Virtual Tour).
The importance of the Painted Desert Inn is that it is a culmination of brilliant architecture by the National Park Service architect Lyle E. Bennett and the artistic skills of Hopi artist Fred Kabotie. On a regional level of significance is its importance as a tangible product and symbol of the work relief programs of the New Deal (NPS, Virtual Tour).
Paleo Indians

There is evidence, mainly spear points, that people as far back as 10,000 BC used the area for hunting big game. Abundant petroglyps can be seen throughout the area and tell of inhabitants that have lived in the desert for thousand of years. Only three areas of the Painted Desert have been surveyed, Petrified Forest National Park, Hopi Buttes, and Homol'ovi, but these three areas show evidence of inhabitation at hundreds of sites (Houk, 1990).



WORKS CITED

Harris, A. G., Tuttle, E., Tuttle, S. D. 1997. Geology of National Parks. Kendall/Hunt Publishing Company. p. 102-112.

Houk, Rose. 1990. The Painted Desert, Land of Light and Shadow. Latrans Books, Prescott, Arizona. 56p.

National Park Service. Petrified Forest Official Map and Guide.

National Park Service. Giant Logs Self Guided Trail.

National Park Service. Petrified Forest National Park Virtual Tours. http://www.nps.gov/pefo/vtour/tourhome.htm

Petrified Forest National Park. http://www.nps.gov/pefo/pefohome.htm

Tweet
More about this author: Thor

From Around the Web




ARTICLE SOURCES AND CITATIONS