Geology and ground water of the Casablanca Basin, Chile

"In the uplands the Cretaceous granodiorite and granite contain water in the weathered zones, and in joints and fractures. These yield small supplies of good water to springs and to shallow domestic and stock wells. The alluvial fill of the lowlands contains a zone of saturation that is sustained by infiltration from rainfall and from the runoff of the uplands.... Where present in the zone of saturation, the coarse-grained members of the alluvial fill yield moderate to large supplies of good water to wells."