Cerro Bayo is a complex volcano on the northern part border between Argentina and Chile. It consists of four overlapping stratovolcanoes along a north-south line. The main volcano fauce is located on the Argentine side, thought the summit of the complex is just west of the border, in Chile. The volcano is about 800,000 years old, but it is associated with ongoing ground uplift encompassing also the more northerly Lastarria and Cordón del Azufre volcanoes. The high summit is the source of two viscous dacitic lava flows with prominent levees that traveled to the north.