natural border. In the north of the Province of Guadalajara, bordering Madrid and Segovia, is a mountain range forming part of the Sistema Central, among which can be distinguished the mountain ranges Pela, Ayllón, Somosierra, Barahona and Ministra, with the headwaters of the rivers Jarama, Cañamares and Henares. The Sistema Central also penetrates the northwest of the Province of Toledo: a southwest to northeast sub-range known as the Sierra de San Vicente, bordered on the north by the Tiétar and on the south by the Alberche and the Tagus, rising up to its maximum heights at the summits of Cruces (1373 m), Pelados (1331 m) and San Vicente (1321 m). On the northwest is the Sistema Ibérico, where there is important fluvial and especially karstic activity, which has given rise to such landscapes as the Ciudad Encantada, the Callejones de Las Majadas and the Hoces del Cabriel. In the southeast is the ridge of the Sierra Morena, the southern border of the Meseta Central and the region's border with Andalusia. Within the Sierra Morena, distinction can be made between the Sierra Madrona, Sierra de Alcudia and Sierra de San Andrés. At the other southern extreme of Castilla–La Mancha, the Sierra de Alcaraz and Sierra del Segura form part of the Sistema Bético. Hydrography The territory of Castilla–La Mancha is divided into five principal watersheds. The Tagus, Guadiana, and Guadalquivir drain into the Atlantic Ocean and the Júcar and Segura into the Mediterranean Sea. The Tagus provides water for some 587,000 inhabitants in a watershed of . It includes the entire province of Guadalajara and the greater part of the province of Toledo, including the two largest cities of the latter province: the capital, Toledo, as well as Talavera de la Reina. The Guadiana watershed extends in Castilla–La Mancha, 37 percent of that river's entire watershed, with a population of 583,259 inhabitants. It includes the southern part of the province of Toledo, nearly all of the province of Ciudad Real (except the very south), the southwest of the province of Cuenca and the northwest of the province of Albacete. The Guadalquivir watershed extends over 5.2 percent of the surface area of the autonomous community, extending through the southern parts of the provinces of Ciudad Real and Albacete, including such important population center as Puertollano. The Júcar watershed had, in 2006, 397,000 inhabitants in an area of , 19.9 percent of the