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Colour graphic illustrating subduction and mountain building process
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The geology of Mount Pleasant Caldera Complex includes a diverse array of intrusive and extrusive rocks resulting from a long history of volcanic activity. Within the caldera rock types include ash flow tuffs, thick sedimentary layers full of angular fragments, and igneous rocks that intrude the volcanic pile. Surrounding the caldera are more ash flow tuffs, lavas, and river-lain sediments.
