The volcano is composed of andesite and rhyodacite lava flows along with pyroclastic flow deposits. It has a basal diameter of about 10 by 12 kilometres (6 mi × 8 mi) and a total volume of about . Along with Cerro Azul, to the south, it lies at the center of a 20-by-30-kilometre (12 mi × 20 mi) volcanic field.