EPOD - a service of USRA
The Earth Science Picture of the Day (EPOD) highlights the diverse processes and phenomena which shape our planet and our lives. EPOD will collect and archive photos, imagery, graphics, and artwork with short explanatory
captions and links exemplifying features within the Earth system. The
community is invited to contribute digital imagery, short captions and
relevant links.
Mantling on Utah’s Hogback Ridge
August 03, 2022
TomMc_EPOD.MantlingHogbackRidgeUtahMcGuire (002)
TomMc_EPOD.LowerCalfCreekFallsMcGuire (4) (002)_a
Photographer: Thomas McGuire
Summary Author: Thomas McGuire
For 5 miles (8 km), Utah’s Route 12. between Escalante and Boulder,
Utah, follows the narrow 1,000 ft (305 m) high Hogback Ridge of
Navajo Sandstone. Spectacular long views on either side of this
highway show tan-to-white-to-yellow Navajo 'slickrock'. The ridge
is also bounded by deep canyons: One is Calf Creek, with two impressive
waterfalls (bottom photo); on the opposite side is Boulder Creek,
with narrow slot canyons.
But there’s a clear sign of something missing. Part of the ridge is
strewn with giant boulders of basalt. Clearly there were lava flows
that covered the Navajo Sandstone along an unknown part of the ridge
and probably much more. For most of the 5 miles (8 km), all that’s left
are the lava-boulders mantling the sandstone.
Basalt is very resistant to weathering and erosion, so it forms the
cap rock of many flat-topped mesas in the Southwest. As the sides of
the mesa erode back, basalt boulders fall from the top and cover the
slopes along with the underlying rock type that make up the body of the
mesa. An observer can be forgiven for thinking the whole mountain is
basalt when the bulk of the bedrock is hidden beneath its thin mantle
of basalt and boulders, which will completely erode away with
(geologic) time. When this happens, there’ll be no record of the lava
flows that once covered significant areas around Hogback Ridge.
Hogback Ridge, Utah Coordinates: 37.8144, -111.4091
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of Reunion Island The Castles of the Calchaquíes Valleys
More...
Geology Links
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* General Dictionary of Geology
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* Mohs Scale of Mineral Hardness
* This Dynamic Earth
* USGS
* MyShake - University of California, Berkeley
* USGS Ask a Geologist
* USGS/NPS Geologic Glossary
* USGS Volcano Hazards Program
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