found south of Chascon. Presently, the Purico complex forms the drainage divide between the Salar de Atacama and the Salar de Pujsa. The high Macon stratovolcano (), Alitar maar () and high Alitar volcano () lie to the south of the main complex. Alitar maar is located is wide and deep. Geology West of South America, the Nazca Plate subducts beneath the South America Plate at rates of . This subduction process along with that of the Antarctic Plate beneath the South American Plate farther south is responsible for volcanism in the Andean Volcanic Belt. Volcanic activity in the region of the Central Volcanic Zone has been ongoing for 200 million years, but with temporal and local variations; 25 million years ago for example it was centered farther east and later moved west. About 23 million years ago, large scale ignimbritic activity commenced in the region with the emplacement of the Oxaya Formation, followed by the Altos de Pica Formation 17-15 million years ago. However, effusive activity of andesitic composition dominated volcanism until the late Miocene. Regional Purico appears to be part of a group of large, caldera-forming volcanic centres that erupted dacitic ignimbrites, a group that is known as the Altiplano-Puna volcanic complex. This group includes the Cerro Guacha, Cerro Panizos, Coranzulí, La Pacana, Pastos Grandes and Vilama centres that cluster around the tripoint between Argentina, Bolivia and Chile. The arid climate of this region means that most volcanic systems are well preserved with little erosion. This complex is underpinned by a magma body at depths of , where arc magmas interact with the crust to form the secondary magmas later erupted by the volcanoes of the Altiplano-Puna volcanic complex. This magma body has been imaged with seismic tomography as a sill-like body and has been named the "Altiplano-Puna magma body". Ignimbritic activity in such systems is episodic, being interrupted by periods with lower volume "steady state" volcanism. The eruption of the Purico ignimbrite is the youngest large ignimbrite eruption in the Altiplano-Puna volcanic complex; the Altiplano-Puna volcanic complex presently is in such a "steady state" stage, but the presence of active geothermal system indicates that magmatic activity is still ongoing. Local Outcrops in the region range in age from Paleozoic to Holocene. The Purico complex formed on top of older ignimbrites such as the Puripicar ignimbrite in the north, the Atana and the La Pacana ignimbrites farther south.