The volcanic rocks at Pasto Ventura are formed by basalt, andesite and basaltic andesite, and define a calc-alkaline suite. Lava flows and lava domes at Pasto Ventura have yielded phenocrysts of amphibole, olivine, plagioclase, pyroxene and xenocryst quartz; basement rocks are present as xenoliths and occur as blocks in maar deposits.