THE SIERRA MORENA  , a range of mountains in

southern Spain . The Sierra Morena constitutes the largest section of the mountain system called the Cordillera Marianica (anc . Monies mariani), which also includes a number of minor Spanish ranges, together with the mountains of southern Portugal . The mean elevation of the range is about 2500 ft., but its breadth is certainly not less than 40 M . It extends eastward as far as the steppe region of Albacete, and westward to the valley of the lower Guadiana . Its continuity is frequently interrupted, especially in the west; in the eastern and middle portions it is composed of numerous irregularly disposed ridges . Many of these bear distinctive names; thus the easternmost and loftiest is called the Sierra de Alcaraz (J9oo ft.), while some of the component ridges in the extreme west are classed together as the Sierras de Aracena . The great breadth of the Sierra Morena long rendered it a formidable barrier between Andalusia and thenorth; as such it has played an important part in the social, economic and military history of Spain . Its configuration and hydrography are also important from a geographical point of view, partly because it separates the plateau region of Castile and Estremadura from the Andalusian plain and the highlands of the Sierra Nevada system, partly because it forms the water-shed between two great rivers, the upper Guadiana on the north and the Guadalquivir on the south . Parts of the Sierra Morena are rich in minerals; the central region yields silver, mercury and lead, while the Sierras de Aracena contain the celebrated copper mines of Tharsis and Rio Tinto (q.v.) .