  
    Aerial photo of a large arroyo cutting through the Sierra San Borja.   | 
    
    The richness of succulents creates a beautiful landscape. See large image for plant list.   | 
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    A grove of boojums.   | 
  
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    Pumice beds support some different species than the surrounding rock substrates. The loose, light gravel holds water well and plants often become very large despite the poor anchorage.   | 
  
  
    
    A large Pachycereus pringlei and Yucca valida in a pumice bed.  | 
    
    Agave shawii is a massive plant that produces an impressive inflorescence (next image). The Ferocactus gracilis in the background is over 8 feet tall.   | 
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      Ferocactus gracilis (top) and the broad-spined var. coloratus.   | 
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