MSGID: 1:317/3 634700c4   
   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.   
      
      
    Arizona’s China Wall   
      
      October 12, 2022   
      
      
       TomMc_ChinaWall   
      
      Photographer:  Thomas McGuire   
      
      Summary Author:  Thomas McGuire   
      
      Shown above is China Wall, a rock formation in the  Tonto National   
      Forest, north of Scottsdale, Arizona. It forms a broken vertical wall   
      nearly a mile long (1.6 km), and about 10 feet high (3 m) and 5 feet   
      wide (1.5 m), draped over the summit of  Bronco Butte (satellite   
      photo below). It was so-named because of its resemblance to the ruins   
      of the  Great Wall of China, which is about two to three times   
      larger.   
      
      China Wall is a sill  intrusion of  rhyolite, a relatively common   
      igneous rock. Rhyolite has a composition similar to  granite, but   
      due to relatively rapid cooling, the crystals are much smaller than   
      granite. The China Wall  magma was injected into meta-sedimentary   
      rocks that are nearly half as old as Earth itself. Although the layer   
      of rock is oriented vertically, it’s inferred that the  sill was   
      injected horizontally and the whole regional package was rotated into   
      the vertical position by a billion years of  plate tectonic forces.   
      With the sparse vegetation found in the U.S. Southwest, bedrock   
      exposures often reveal the orientation of the layers.   
      
       TomMc_ChinaWall.jpg2b   
      
      
      China Wall, Arizona Coordinates: 33.9008, -111.8810   
      
      
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       More...   
      
   Geology Links   
      
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        *  Geologic Time   
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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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