The region of Castilla y Leon includes much of northern Spain. Castilla y Leon borders Asturias and Cantabria in the North, the Basque Country, La Rioja, Aragon, Castilla la Mancha and Madrid in the East, Extremadura and Castilla la Mancha in the South; and Portugal and Galicia in the West. Castilla y Leon belongs to the lower northern plateau with the exception of the north eastern province of Burgos that is lies in the Ebro depression. The whole area is surrounded by mountains. There are notable foothills arising from the Cantabrian mountain range in the north. The Leon Mountains, also in the North, lie in the shadow of these mountains. The Iberian mountain range rises from the northeast, with numerous sierras crossing over into the region. The Sistema Central range appears in the South, and includes both the sierras of Gredos and Guadarrama. The high plateau plain, lies in the middle of these mountains encircled by lesser mountain ranges. These mountain peaks reach up to 500 and 1000 Mts. in height. The most important waterway is the river Duero that begins in the province of Soria, crosses the region and then heads into Portugal where it finally flows into the Atlantic. Two other important tributaries from the Tagus, the Tietar and the Alberche also begin their life in the province.