Based on deep well data, the authors determined the existence of a strutural high on the summit of basaltic flows located in the strech between Tanabi and Votuporanga in the northwestern region of the State of São Paulo The presence of this struture, connected to tectonic phenomena of pre-Bauru age and responsible for the contours of basaltic substratum, exercised a profound influence on the sedimentation of the Bauru Group, being responsible for the variations of thickness, spatial behavior and the hydrological properties of the sediments of the area.
