The region is dominated by the Altiplano-Puna volcanic complex, where during the Miocene-Pleistocene epoch large ignimbrite eruptions occurred. In the present day, volcanism is of andesitic composition forming volcanic cones. Activity is controlled by fault zones, some of these linked to the Pastos Grandes caldera. Neighbouring volcanoes with similar characteristics to Cerro Chao include Cerro Chanca/Pabellon, Cerro Chascon-Runtu Jarita complex, Cerro Chillahuita and La Torta. Cerro Chao lies within a northwest-running belt of volcanoes known as the San Pedro-Linzor volcanic chain, some of them over high, of which San Pedro has historical activity. Cerro Chao is the largest such silicic lava flow known.