The top of the hill is capped with basalt. Erosion has removed most of the basalt from the area, but left this resistant hill. Beneath the basalt is thin layer of Moenkopi Sandstone and beneath the sandstone is Kaibab Formation. As you walk around the hill a large depression will come into view. This depression is a sinkhole called Citadel Sink.
This sink began with the formation of an underground network of caverns in the Kaibab Formation similar to those below the Wuptaki Blowhole. Weakly acidic groundwater percolated through the rocks and slowly dissolved the limestone of the Kaibab Formation forming a cavern. The cavern grew so large that it could no longer support the weight of the rocks above it and collapsed forming the sinkhole.
Logging requirements:
Send me a note with :
- The text "GCZ5W5 Citadel Sink - Wupatki NM" on the first line
- The number of people in your group.
- Send me a note with your explanation as to why this hill sits above the surrounding land. Be specific with names or types of rocks.
- Photos are appreciated with your log.
Editorial review provided by Sara Hanson.
The above information was compiled from the following sources:
- Hanson, Sarah L. 2003, Roadside Geology: Wupatki and Sunset Crater Volcano National Monuments, Arizona Geological Survey, Down-to-Earth 15
- California State University at Long Beach, 2006, Environmental Clues in Sedimentary Rocks, http://seis.natsci.csulb.edu/bperry/Sedimentary%20Rocks%20Tour/environmental_clues.htm
Placement approved by the
Wupatki National Monument