MSGID: 1:317/3 62eab7e2   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    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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       Mantling on Utah’s Hogback Ridge  Dendrite Inclusion in Opal   
       New Eddystone Rock  Varvite Park in Brazil  Volcanic Tunnels   
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       More...   
      
   Geology Links   
      
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        *  This Dynamic Earth   
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        *  MyShake - University of California, Berkeley   
        *  USGS Ask a Geologist   
        *  USGS/NPS Geologic Glossary   
        *  USGS Volcano Hazards Program   
      
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