The Great Arch in Zion National Park is a large blind arch in the Navajo Sandstone. A blind arch is an arch of rock still attached to the rock face. It stretches about 600 feet across and about 400 feet high.
One of the possible ways a blind arch can form is from the undermining of the sandstone cliffs. In Zion Canyon, springs often form at the bottom of the Navajo Sandstone just above the shale of the Kayenta Formation (see Weeping Rock). These springs erode the shale out from underneath the sandstone leaving the sandstone unsupported. Large chunks of sandstone eventually fall off, usually without patter. However, sometimes the upper layers of the sandstone don’t break off and form an arch. Eventually this portion will also break off.
Blind arches are relatively common throughout the park.
Send me a note with :
- The text "GCZ5Z2 Blind Arch - Great Arch of Zion" on the first line
- The number of people in your group.
- Look at the rock material beneath the blind arch. What is your opinion as to whether the material came from under the arch (making the arch deeper) or if it came from the arch (making it taller) and your reasoning. .
- Optional--because some are logging this cache without stopping to look, please post a picture of yourself or other member of your group with the arch in the the background.
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
- DesertUSA, The Ultimate Desert Resource, http://www.desertusa.com/zion/du_znpdesc.html
Placement approved by the
Zion National Park