Andalusian Plain is bounded on the north by the Sierra Morena and on the south by the Sistema Penibético; it narrows to an apex in the east where these two mountain chains meet. The Ebro Basin is formed by the Río Ebro valley, contained by mountains on three sides—the Sistema Ibérico to the south and west, the Pyrenees to the north and east, and their coastal extensions paralleling the shore to the east. Minor low-lying river valleys close to the Portuguese border are located on the Tagus and the Río Guadiana. The Coastal Plains regions are narrow strips between the coastal mountains and the seas. They are broadest along the Golfo de Cádiz, where the coastal plain adjoins the Andalusian Plain, and along the southern and central eastern coasts. The narrowest coastal plain runs along the Bay of Biscay, where the Cordillera Cantábrica ends close to shore. The islands The remaining regions of Spain are the Balearic and the Canary Islands, the former located in the Mediterranean Sea and the latter in the Atlantic Ocean. The Balearic Islands, encompassing a total area of 5,000 square kilometers, lie 80 kilometers off Spain's central eastern coast. The mountains that rise up above the Mediterranean Sea to form these islands are an extension of the Sistema Penibetico. The archipelago's highest points, which reach 1,400 meters, are in northwestern Mallorca, close to the coast. The central portion of Mallorca is a plain, bounded on the east and the southeast by broken hills. The Canary Islands, ninety kilometers off the west coast of Africa, are of volcanic origin. The large central islands, Tenerife and Gran Canaria, have the highest peaks. Pico de Las Nieves, on Gran Canaria, rises to 1,949 meters, and the Teide, on Tenerife, to 3,718 meters. Teide, a dormant volcano, is the highest peak of Spain and the third largest volcano in the world from its base. Drainage, floods, and water stress Of the roughly 1,800 rivers and streams in Spain, only the Tagus is more than 960 kilometers long; all but 90 extend less than 96 kilometers. These shorter rivers carry small volumes of water on an irregular basis, and they have seasonally dry river beds; however, when they do flow, they often are swift and torrential. Most major rivers rise in the mountains rimming or dissecting the Meseta Central and flow westward across the plateau through Portugal to empty into