sentences:  The complex has therefore been described as a caldera or a cauldron subsidence.Heavy erosion of the volcanic rocks has exposed a series of biotite-quartz-porphyry, biotite quartz-feldspar-porphyry and quartz monzonite subvolcanic plutons and dike swarms.They intrude through fractured and hydrothermally altered Mesozoic to early Tertiary granitic and metamorphic rocks of the Coast Plutonic Complex.