city, northern Chile, on the Río Loa in an extremely arid region. It lies on the western slope of the Andes at an altitude of 7,435 feet (2,266 metres) and is linked to Antofagasta, 125 miles (200 km) southwest, by aqueduct. The oasis city is a service centre for the Chuquicamata copper mine and an agricultural marketing centre. The Smithsonian Institution (U.S.) operates a solar observatory nearby. Pop. (2002) 126,135.