The River Ruecas flows for about two kilometres northeast of the town of Cañamero within a deep defile flanked by the high quartzite crests of the Sierra de los Castillejos, the Sierra de la Lóriga, and the Risco del Castillo and the Risco de las Cuevas. Halfway along this route it is joined by the waters of the Arroyo Valbellido, which drains one of the most fertile valleys of the municipal district
The River Ruecas flows in a gorge from the dam of the Cancho del Fresno reservoir to the start of the fertile plain of the Huertos del Río. The width of the landscape means that access is possible from different roads; from the Cañamero to Guadalupe road that runs parallel to the river, from the old Berzocana road that also leads to the aforementioned dam, and along the road to the cave painting site known as the Cueva de Álvarez. The defile can also be reached via the Camino Natural de las Villuercas from the quarter of La Jarilla at the highest part of the town of Cañamero.
The encasing of the River Ruecas between the hard “Armorican quartzites” was caused by fluvial erosion on a large tectonic fault that runs along the bottom of the cutting in a SE-NW direction. This divides into two parts the narrow Cañamero anticline, the folded quartzite strata of which can be observed at the Risco de las Cuevas.
This narrow anticline extends from here to the Apreturas del Almonte via sites of geological interest such as the Sierra de la Madrila of Cañamero, the Canchos de las Sábanas of Berzocana, the Cancho del Reloj of Solana, and the Castle of Cabañas. Together with the discontinuous Cañamero-Sierra de Berzocana syncline, it represents the western limit of the great tectonic megastructure of the Santa Lucía-Rio Ruecas syncline in its contact with the Precambrian shales of the great Logrosán anticline (see geological map) in the form of a reverse fault. The Armorican quartzites of these folded structures contain a multitude of trace fossils of Palaeozoic marine animals (Cruziana, Skolithos, etc.), together with other sedimentary traces produced by the waves (ripple marks).
The beauty of the landscape of the Cañamero anticline and the gorge of the River Ruecas is complemented by that of its cave shelters such as those of the Cueva de Álvarez or Cueva de la Chiquita, the Cueva de Rosa, the Abrigo de los Vencejos, etc.. These sites were temporarily occupied as shelters and sanctuaries by the peoples of the Chalcolithic period (3500 years ago), who produced numerous cave paintings of stylised reddish and black figures of men and animals, star signs, dashes and dots, etc.
The physical characteristics of the river gorge also encouraged the settling of Chalcolithic settlements and during the Reconquest the construction of the impregnable Muslim castle of Cañamero, where the followers of the prince of León Sancho Fernández were billetted in 1220. As from the Middle Ages numerous staggered flour mills were built in the narrow valley to take advantage of the driving force of the waters of the River Ruecas; some of these have curious legends related to the trace fossils (Cruziana) engraved in the quartzites of the watercourse. It is also possible to visit the Interpretation Centre of the Sierra de las Villuercas and the Guadarranque Valley Special Bird Protection Area (Zona Especial de Protección de Aves, ZEPA), which is very near the Cancho del Fresno dam.