Abstract
The studied area, about 2000 km2, is covered in its central part, by the Las Estacas Formation from the late Pleistocene (Qpe). These rocks consist mainly of anhydrites and "caliche". They are surrounded by mountain ranges of Cretaceous limestones and sandstones.
The hydrogeological characteristics of the exposed areas and from a hydrogeochemical point of view, three aquifers can be detected. The first one is developed in evaporites and debris. The second formed by the interdigitation of sandstones and limestones, generating less salty water; and finally the third is emplaced in the Cretaceous limestones and sandstones.
The water from the Las Estacas Formation is supplied by the underlaying Cretaceous rocks and by direct infiltration of pluvial precipitation. This formation has several small depressions that contribute to an effective reload and prevent the active erosion of the area. This fact is proved by the lack of gullies and by the insignificant depth of the existing ones. This fact is believed to be important considering the lack of cohesion of this formation.
The maximum thickness of the evaporites of the Las Estacas Formation is about 30 m it pintches out along the borders of the basin and towards the topographic highs. The existence of evaporites certifies the endorreic character of the basin and the dry climate during the late Pleistocene. Bassed upon 54 chemical analyses of water samples, the existence of four different families of water was established. This interpretation is supported by semilogarithmic diagrams.
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