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Little
Egypt Geologic Site
Hoodoos of Garfield County
by Mark Milligan
Geologic Information: Why travel around the world when Little
Egypt is as close as Garfield County? This geologic area showcases
fantastic and sometimes grotesque stone hoodoos that bring to mind
the magnificent temples of ancient Egypt, hence its name Little
Egypt Geologic Site.
Geologically however, the area is more like Goblin Valley State
Park and Cathedral Valley of Capitol Reef National Park. Weathering
and erosion carves hoodoos (i.e., Egyptian temples, goblins, and
cathedrals) in all three areas from the Entrada Sandstone. This
is the same formation that also erodes to arches, fins, and spires
in Arches National Park.
Temples in the Entrada Sandstone at the Little Egypt
Geologic Site.
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Joint sets (fractures) within the Entradas fine-grained sandstone
beds play an important role in hoodoo development by creating initial
zones of weakness. Unweathered joints intersect to form sharp edges
and corners.
These edges and corners are more susceptible to weathering because
they have a greater surface-area-to-volume ratio than the faces.
As a result, they weather more quickly, producing rounded hoodoos
through a process called spheroidal weathering.
Spheroidal weathering helps shape the hoodoos, but it is only part
of the larger erosion process that forms and exhumes the hoodoos.
Interbedded and underlying shale and siltstone beds are less resistant
to weathering and erosion than the hoodoos sandstone beds.
Combined with spheroidal weathering of the sandstone beds, these
softer shale and siltstone beds can give the hoodoos a stacked appearance,
elongated shapes, and flat bottoms.
Additionally, variation in the amount and type of cementation
(between grains in sedimentary rocks) may act as a secondary control
on the unusual shapes of individual hoodoos.
Similar to rocks all across southeastern Utah, the Entradas
reddish hue comes from minute quantities of hematite (iron oxide).
The whiter areas result from bleaching by ground water that chemically
removed the hematite (or rendered it colorless) before the rocks
were exhumed by erosion.
How to get there: From Hanksville, head south on State
Route 95. Approximately 4.2 miles after (south) the Garfield County
line, just past (south) mile marker 20, turn right (west) on the
Scenic Backway road towards North Wash. Just off the
highway is a sign to Little Egypt Geologic Site. Little
Egypt is less than two miles off the highway.
Geosights article, Survey Notes,
v. 34 no. 2, June 2002
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