Corrida de Cori volcanism is calc-alkaline and consists of potassium rich andesite as well as basaltic andesites. The Cerro Escorial ignimbrite may be of crustal origin and is dacitic.: Trachydacite is found at Cerro Negro. The basement beneath Corrida de Cori is mostly buried, but occasional outcrops indicate Paleozoic granites and sedimentary and volcanic rocks.