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Columnar Jointing 
Columnar jointing occurs when lava or magma cools and contracts quickly enough to cause jointing. The rock takes on the appearance of columns, which generally form perpendicular to the local isotherm (areas of equal temperature). These columns may be on a scale of a foot to hundreds of feet long. Columnar jointing is especially common in basaltic lava flows.

  A close-up of Columnar jointing  near North Pass on CO-114.  This commonly forms as basalt, or andesite magma cools and contracts at the surface or very shallow underground.
These columns formed in the basalt-like flows of shoshonite on South Table Mountain as the lava cooled and contracted.

 Colorado Geological Survey
Last Updated: 1/24/2013 2:40 PM 
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