The Llano de Chajnantor is located on the western side of the Puna de Atacama, which is another name for the southern part of the Altiplano. The main ridge of the Andes is over to the east, well into Argentina. The Salar de Atacama basin borders the Puna de Atacama to the west, which in turn is bordered by the Cordillera Domeyko. The western side of the Puna de Atacama is dotted with the volcanoes of the Central Volcanic Zone of the Andean Volcanic Belt. The Llano de Chajnantor site itself is bounded by volcanic peaks of the Purico Complex, which have been active in the Holocene but have not erupted in historic times. Cerro Chajnantor is to the north, Cerro El Chascón to the east, and smaller peaks to the south and west. The Pampa la Bola lies to the northeast, north of Cerro El Chascón and east of Cerro Chajnantor. Llano de Chajnantor has an average elevation of , while Pampa la Bola averages . The thin atmosphere makes work difficult for humans, so much of the activity for ALMA will be conducted at a base camp in the Salar de Atacama basin at approximately in elevation.