Cochise College Student Papers in Geology

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Roger Weller, geology instructor

Hoodoos
Linda Wright
Historical Geology

Spring 2006

         My choice for a term paper in Historical Geology is centered on the Colorado Plateau which takes up the four corners in the United States, Arizona, Colorado, New Mexico and Utah. The Colorado Plateau is a large subject, but to pick just one place, it would be Bryce Canyon in Utah for it’s fantastic, ten-story buildings sized sedimentary rock pillars.

Common Name (preferred):    Hoodoo, goblin
Geologic Name: Hoodoo
Size Range: 5-150 ft. tall (1.5-45 m)
Formation Name: Clarion Limestone
Rock Age: Paleocene or Eocene in age, 40-60 mya
Famous Examples: Thor's Hammer, The Hunter, Queen Victoria

          Hoodoos are tall spiny spires of rock that protrude from the bottom of arid basins and "broken" lands. Hoodoos are commonly found in the high plateaus region of the Colorado Plateau and in the Badlands regions of the northern Great Plains. Scattered throughout the region, there is nowhere in the world they are as thick as in the northern section of Bryce Canyon National Park.

Hoodoos are composed of soft sedimentary rock, and are topped by pieces of harder, less easily-eroded stone that protects the columns from the elements. Hoodoos have a variable thickness and are often described as having a "totem pole shaped body."

The name given to the rock layer that forms Hoodoos at Bryce Canyon is the Clarion Formation. This layer has many rock types including siltstone and mudstone and is predominantly limestone. Thirty to forty million years ago this rock was "born" in an ancient lake that covered a great deal of western Utah. Mineral deposits of different rock types cause Hoodoos to have different colors throughout their height.

One might ask how these huge chess like forms are made, are they carved out by humans or animals or could they be a product of Mother Nature?

Hoodoo formation in Bryce Canyon

Hoodoos in the Bryce Canyon area are formed by two weathering processes that continuously work in eroding the edges of the Paunsaugunt Plateau. The main weathering force at Bryce Canyon is frost wedging where there are over 200 freeze and thaw cycles a year. In the winter, there is melting snow and water that seeps into the cracks and freezes at night. When water freezes it expands by almost 10%, little by little prying and opening cracks, making them ever wider the same way a pothole forms in a paved road.

What little rain falls in the area is how the hoodoos are sculpted. Rainfall in Bryce Canyon is slightly acidic. This weak carbonic acid can slowly dissolve limestone grain by grain. This process is what rounds the edges of hoodoos and gives them their lumpy and bulging profiles.

Where the interior mudstone and siltstone layers seem to interrupt the limestone, the rock will be more resistant to the chemical weathering due to the comparative lack of limestone. Many of the hoodoos are topped with a type of magnesium-rich limestone, dolomite. Rain is one of the main sources of erosion that is the actual removal of the debris. In the summer, monsoon type rainstorms pass through Bryce Canyon region bringing short flash flood and high intensity rain.

Hoodoos time span is short lived; the same processes that create hoodoos, also eventually destroy them. In the case of Bryce Canyon, the hoodoos' rate of erosion is measured at two to four feet every 100 years.

Hoodoo colors are more brilliant after a rainstorm. With all the seasons winter is especially unique. Not only does melting snow paint the colors, the bedspread of white adds another dimension to the breath taking beauty under the crisp blue sky.

Next one might ask, when did they begin to form, were there humans or dinosaurs wondering around in them?

As North America gradually drifted northward the climate cooled and then became wetter. Eventually headward erosion of the Paunsugunt Plateau in the late Tertiary and early Quaternary time created Bryce Canyon's amphitheaters and differential erosion and frost wedging created the hoodoos.

The exposed geology of Bryce Canyon area is a record of deposition which covers the last part of Cretaceous period and the beginning of Cenozoic era in this part of North America. The Canyon varied from a warm shallow sea in which Dakota sandstone and tropic shale were deposited in the cool lakes and streams, which contributes to the colorful Clarion formations, hoodoos.

Minor events continued through the start of the Cenozoic and were accompanied by some basaltic eruptions and mild deformation. These sediments were laid down in these cool streams and lakes.

This map will show the reader an easy way to travel through Bryce Canyon National Park with marked places of interest.

Bryce Canyon is a beautiful place to see, and walk through, to stand above the hoohoos looking down over them, and to marvel at their size. It is amazing to stand next to one, looking up towards the sky, studying its incredible structure. To view them from a distance, wet from rain and snow, the sun, like a delicate paint brush bringing out the breath taking colors as it moves through the sky. Bryce Canyon is a wonderful place for a Historical Geology study.

Earth System History, Steven M. Stanley, (W.H. Freeman and Company; 1999), pages 511-513, 537 ISBN 0-7167-2882-6

Annabelle Foos, Geology of the Colorado Plateau, National Park Service PDF Accessed 12/21/2005.

For resources and information on teaching geology using National Park examples, see the Students & Teachers pages.