The greatest average elevation in Spain is found in the centre, in Castile and Extremadura, whence there is a descent, by great steps as it were, to the east and to the west. On the eastern side the descent is short and rapid to the Mediterranean Sea. On the west, the land falls by longer and more gradual slopes to the Atlantic Ocean, so that central Spain may be said to look geographically toward the west. There is an even more gentle decline from the base of the Pyrenees to the valley of the Guadalquivir, although it is interrupted by plateaus which rise above the general level. All of these gradients are modified greatly by the mountain ranges within the peninsula. The Pyrenean range not only separates France from Spain, but also continues westward under the name Cantabrian Mountains for an even greater distance along the northern coast of the latter country, leaving but little lowland space along the sea, until it reaches Galicia in the extreme northwest. Here it expands until it covers an area embracing northern Portugal as well. At about the point where the Pyrenees proper and the Cantabrian Mountains come together the Iberian, or Celtiberian, range, a series of isolated mountains for the most part, breaks off to the southeast until near the Mediterranean, when it curves to the west, merging with the Penibética range (better known as the Sierra Nevada Mountains, the name of that part of the range lying south of the city of Granada), which moves westward near the southern coast to end in the cape of Tarifa. [Sidenote: Geographical divisions of the peninsula.]