Northernmost Chile is home to a well-preserved disequilibrium landscape of great antiquity. Contrasting drainage patterns are developed on the western slope of the Altiplano plateau. The oldest of these patterns is a now-relict parallel-patterned drainage network. In places a younger pattern, comprising a series of deeply incised canyons, or quebradas, crosscuts the older parallel-patterned network. These canyons show strong evidence of a groundwater-sapping origin. We hypothesize that the initiation of the canyon network resulted from changes in the hydrological regime related to a drying out of climate of the forearc and to the uplift of the Altiplano plateau.