The chain extends in an almost straight line 270 mi (435 km) from the Bay of Biscay on the west to the Mediterranean Sea on the east; its maximum width is c.80 mi (130 km). About two thirds of its area is in Spain. Of the three main ranges of the Pyrenees, the central section is the highest. The Pico de Aneto, Spain (11,168 ft/3,404 m), is the tallest peak; other peaks include the Pic de Vignemale and the Pic du Midi d'Ossau (France) and Monte Perdido (Spain). The Cantabrian Mts. are a western extension of the Pyrenees. The Pyrenees were formed during the Tertiary period. Exposed crystalline rock is found in the uplands, while folded limestone composes the lower slopes. Glaciated in the distant past, the Pyrenees do not have any glaciers now. The permanent snowline is at an elevation of c.6,000 ft (1,830 m).
Characteristic of the French Pyrenees, which are much steeper than the southern slopes, are the torrents called gaves, often falling in cascades, and the natural amphitheaters known as cirques, notably the famous Cirque de Gavarnie. The more important rivers—the Garonne, the Aude, and the Adour—run north; among the Spanish rivers rising in the Pyrenees are the Aragón, the Cinca, and the Segre. The Pyrenees are a climatic divide. The northern slopes receive abundant rainfall while the southern slopes have a steppelike climate.