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| The striated surface of Devils Tower reflects the polygonal shaped fractures (columnar joints) that formed as the igneous material in the conduit (or neck) of the igneous body contracted as it cooled after intruding the sedimentary rocks of the Powder River Basin. Erosion has removed overburden, so whether Devil's was only an intrusive body or a volcano is unknown (Lageson and Spearing, 1988; NPS, 2008). |
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