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Received 3 April 2007; Revised 14 May 2007; Accepted 21 May 2007 this goal, the “La Venta” Geographical Association performed a study from 1999 to 2003 (Bernabei et al., 2002; Forti et al., 2003). This paper describes the geomorphic aspects of karst landforms and caves surveyed during the field investigation, which testify to an ancient bathyphreatic regional flow of thermal and meteoric waters, probably similar to that which feeds the present springs (Forti et al., 2004b). STUDY AREAGeographical features The Sierra Madre Oriental crosses the state of Coahuila from N to S, with a series of parallel mountain ridges, which enclose fluvio-lacustrine intermontane flats of different extension. The Cuatro Cienegas plain is one of these flat areas. It extends over an area of about 840 km 2 and is located at 27° N and 102° W, at an altitude of about 700 metres. The high sloping walls of the Sierra Madera, which reach an altitude of 3020 m a.s.l., and the lower Sierra Menchaca, form the northern boundary of the area. The Sierra San Vincente and Sierra La Purisima border the plain on the eastern side. The southwestern boundary is the Sierra La Fragua, whereas the Sierra San Marcos y Pinos divides the Cuatro Cienegas plain into two parts in its southern part (Fig. 1). All these mountains consist mainly of Cretaceous limestone folded into long asymmetric anticlines. Their more steep slopes, usually the southwestern sides, often show vertical or overturned beds. Steep slopes and vertical walls are deeply cut by longitudinal and transverse streams, which together form a typical “trellis” pattern. The northeast-facing slopes, many of which correspond to International Journal of Speleology 36 (2) 83-92 Bologna (Italy) July 2007

The polygenetic caves of Cuatro Ciénegas (Coahuila, Mexico): morphology and speleogenesis