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Double Arch Alcove in Crossbedded Sandstone EarthCache

Hidden : 11/16/2007
Difficulty:
2 out of 5
Terrain:
3.5 out of 5

Size: Size:   not chosen (not chosen)

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Geocache Description:

The Double Arch at the end of the Middle Fork Taylor Creek Trail shows two ways that arches form.

The Taylor Creek Trail is one of the most popular in the Kolob section of Zion National Park. After a short steep decent the easy trail follows the creek up to the arches crossing it many times. In the summer the creek is almost dry, but in the winter and spring, expect to get wet.

There is sign asking you not go further than the base of the slopes beneath the alcoves. Please respect this sign as it is there to protect the fragile slopes and plants beneath the lower arch. There are what look to be trails that go up the sides, but these are not stable and contribute to the erosion of the area.

As you go up the canyon, expect to loose gps reception, but don’t worry, there is nowhere else to go. At the coordinates, you can get reception if you sit in one spot for 5 or 10 minutes.

These two arches have formed in the cross-bedded Navajo Sandstone. Two different erosional processes have resulted in similar geomorphological features. In one, natural fractures in the rock called joints provide space for water to collect in. The water freezes, expands and pushes boulders off the cliff. In the other, ground water dissolves the cement holding the sand together and seeping out of the rock in a spring.

Crossbeds N37 27.491 W113 09.766
The crossbeds in the Navajo Sandstone can be seen in the northern cliffs right at ground level. Cross-beds are formed by layers of sand grains as they build up into a dune then collapse. Wind piles sand up the gentle windward side of a dune. When the dune becomes too steep to support itself, it collapses creating the angled layers. This process also slowly inches the dune in the direction of the wind.

Over time, the next dune migrates over the first, burying the first and preserving the crossbeds. The USGS Western Coastal & Marine Geology website has some downloadable movies to demonstrate the process (http://walrus.wr.usgs.gov/seds/Movie_list.html). Image Source USGS: http://www2.nature.nps.gov/geology/usgsnps/dune/dune.html

Logging requirements:
Send me a note with :

  1. The text "GC17E2D Double Arch Alcove in Crossbedded Sandstone" on the first line
  2. The number of people in your group.
  3. the erosional process that predominates in each of the arches
  4. based on only the crossbeds you see, which way was the wind blowing when the sand was deposited.

The above information was compiled from the following sources:

  • Miek, Robert F., et. al., Geology of Zion National Park, Utah in Geology of Utah’s Parks and Monuments, 2003 Utah Geological Association Publication 28 (second edition) D.A. Sprinkel, T.C. Chidsey, Jr. and P.B. Anderson, editors

Placement approved by the
Zion National Park


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