Common Name (preferred): Hoodoo, goblin
Geologic Name: Hoodoo
Size Range: 5-150 ft. tall (1.5-45 m)
Formation Name: Claron Limestone
Rock Age: Paleocene or Eocene in age, 40-60 mya
Famous Examples: Thor's Hammer, The Hunter, Queen Victoria
At Bryce Canyon, hoodoos range in size from that of an average human to heights exceeding a 10-story building. Formed in sedimentary rock, hoodoo shapes are affected by the erosional patterns of alternating hard and softer rock layers. The name given to the rock layer that forms hoodoos at Bryce Canyon is the Claron Formation. This layer has several rock types including siltstones and mudstones but is predominantly limestone. Thirty to 40 million years ago this rock was "born" in an ancient lake that covered much of Western Utah. Minerals deposited within different rock types cause hoodoos to have different colors throughout their height.
In addition to frost wedging, what little rain we get here also sculpts the hoodoos. Even the crystal clear air of Bryce Canyon creates slightly acidic rainwater. This weak carbonic acid can slowly dissolve limestone grain by grain. It is this process that rounds the edges of hoodoos and gives them their lumpy and bulging profiles. Where internal mudstone and siltstone layers interrupt the limestone, you can expect the rock to be more resistant to the chemical weathering because of the comparative lack of limestone. Many of the more durable hoodoos are capped with a special kind of magnesium-rich limestone called dolomite. Dolomite, being fortified by the mineral magnesium, dissolves at a much slower rate, and consequently protects the weaker limestone underneath it in the same way a construction worker is protected by his/her hardhat.
Rain is also the chief source of erosion (the actual removal of the debris). In the summer, monsoon type rainstorms travel through the Bryce Canyon region bringing short duration high intensity rain.
Unfortunately hoodoos don't last very long. The same processes that create hoodoos are equally aggressive and intent on their destruction. The average rate of erosion is calculated at 2-4 feet (.6-1.3 m) every 100 years. So it is that Bryce Canyon, as we know it, will not always be here. As the canyon continues to erode to the west it will eventually capture (perhaps 3 million years from now) the watershed of the East Fork of the Sevier River. Once this river flows through the Bryce Amphitheater it will dominate the erosional pattern, replacing hoodoos with a "V" shaped canyon and steep cliff walls typical of the weathering and erosional patterns created by flowing water. Indeed a foreshadowing of this fate can be observed in Water Canyon while hiking the Mossy Cave Trail. For over 100 years a diversion canal has been taking a portion of the East Fork of the Sevier River through this section of the park and already it's easy to see the changes the flowing water has created.
While we can't stop this inevitable fate, humans can help to preserve the Park's existing hoodoos by keeping to the park trail system. Believe it or not, just walking up to the base of a hoodoo will shorten its life span as your tracks weaken the clay slopes that protect the hoodoo's foundations. Staying on established trails ensures that erosion will not prematurely destroy the hoodoos that millions of people come from all over the world to see.
When and where to see at Bryce:
Hoodoo colors are more vibrant after a rainstorm. Viewing hoodoos in the winter is especially rewarding. Not only does melting snow enrich the colors but the blanket of white adds another dimension to the beauty under the crisp blue sky.
Kiver, Eugene P., Harris, David V. 1999. Geology of U.S. Parklands 5th ed. John Wiley & Sons, Inc. 522-528.
Sprinkel, Douglas A., Chidsey, Thomas C. Jr., Anderson, Paul B. 2000. Geology of Utah's Parks and Monuments. Publishers Press: 37-59