moraines from glaciers in its highest part. It also features large karstic areas. Nevertheless, some of its glacial valley characteristics have been modified in some points by the torrential nature of the Miera River near its source. The higher basin of the Miera has an abrupt relief, not suitable for the human habitat. In spite of that, caves with prehistoric settlements have been discovered in Piélagos, Rascaño and Salitre, one of the highest altitude (450 m over sea level) stations with paleolithic art. The medium valley of the Miera River, that mostly coincides with the municipality of Miera, is trapped between the abrupt karstic limestone pavements of Porracolina to the East, and Las Enguizas to the West, both belonging to the Urgonian Complex. In both limestone blocks, important karstification phenomenons take place; there have been relevant explorations in these complexes and solved labyrinths in the caves of Alto del Tejuelo. Between them flows the Miera River, through the Escudo de Cabuérniga fault; with a diapir appearing from it between the villages of Linto and Miera and breaking the geologic continuity of the river course. The chalky mountain mass of Las Enguizas sits directly over the silicon materials of the Early Cretaceous that make the hydrologic base of its four most important hydrologic systems and its cavities, partially studies in the case of El Cuevo de Noja-Fuente Fría and the Castrejón-Cubillo del Machorro network. They are structurally simpler systems than those of Porracolina, because the slope of the waterproof lower-cretaceous base has generated alignments perpendicular to the valleys axis. In the lower course the most remarkable spots are the caves with prehistoric occupation: La Fuente del Francés (Hoznayo), La Garma (Omoño) and Los Moros (San Vitores). During the 16th century the economic life of this valley was focused around the lower course, towards Liérganes; years later in the 18th century a small industry had been established with the Royal Artillery Factory of La Cavada, which supplied weapons to the ships built in the Guarnizo and Colindres shipyards. This zone gave many emigrants to Andalusia and the Indies. It is a cradle of many distinguished Indianos like Juan de la Cuesta Mercadillo, who was the builder of the La Rañada Palace in Liérganes; Ramón Pelayo de la Torriente (Marquis of Valdecilla), who developed many important constructions in the region and other points of Spain during the first third of the 20th century,