The region of Extremadura lies in the south western part of Spain, and borders Castilla y Leon in the North, Castilla la Mancha in the East, Andalucia in the South, and Portugal in the West. Most of Extremadura is made up of vast stretches of plains with an average height of around 350 Mts. There are three mountain formations in the region. The Sistema Central in the North mainly comprises of Gredos sierra, Gata sierra, Francia sierra, Plasencia sierra and Vera sierra. They are high mountains; some reaching almost 2,000 Mts., with deep gorges heading South such as Jaranda, with High Mountain passes that include Bejar and Tornavacas. The highest peak in the area is Calvitero that reaches 2,425 Mts. The second mountainous area is the central area that is penetrated by the mountains of Toledo, the highest peak of which is Las Villuercas measuring 1,601 Mts. The third area in the south of the region belongs to the Sierra Morena mountain range. They are the lowest mountains in the region. The highest peak is Tentudia, at 1,140 Mts. The most notable river valleys include Jerte and Tietar, La Vera and Las Hurdes, as well as Ambroz valley. Two major rivers criss-cross the region and filter the waters from other lesser rivers in the area. The rivers are the Tagus, which travels through Caceres, finally entering Portugal, and the Guadiana, that encompasses all of Badajoz within its basin and heads South, forming a natural border with Portugal. The rivers in the region of Extremadura are governed by the various reservoirs in the area, that form a vast hydrological network that supplies water for crops, for generating electricity and for general consumption by the inhabitants. Valdecañas, Torrejon-Tagus, Alcantara, Gabriel and Galan are the reservoirs that lie in the Tagus river basin. Cijara, Puerto Peña (Garcia Sola), Orellana and La Serena are some of the different reservoirs that can be found in Guadiana's basin. La Serena reservoir, in the river Zujar, is the largest in Spain and the second largest in Europe.