This paper gives a summary account of the geology of parts of the Atacama Desert, northern Chile, between Parallels 22° and 26° S. Precambrian, Upper Paleozoic, Mesozoic, and Upper Tertiary rocks are displayed in the region. Precambrian metamorphics crop out in isolated exposures at the southern foot of the Limon Verde Range. Upper Paleozoic sedimentites form the eastern half of the ranges between Toco and Tocopilla. Volcanic rocks, belonging to three different cycles of Upper Triassic-Lower Liassic, Malm-Neocomian, and Senonian age, respectively, are very extensively developed. These sequences contain intercalations of marine and continental sedimentites, exposed in isolated areas, and are intruded by Senonian granodiorites. The Jurassic and Cretaceous sediment ry sequences exposed at Moctezuma, Caracoles, Potrerillos-Pedernales, Purilactis, Sierra de Almeida, and El Way are described in some detail. The eastern part of the region is formed of Upper Tertiary continental beds and volcanic rocks. The Miocene-Pliocene sequence of the San Pedro de Atacama area is briefly described.