They stretch for over 300 km (180 miles) across northern Spain, from the western limit of the Pyrenees to the Galician Massif in Galicia, along the coast of the Cantabrian Sea.

In some parts the coastal range rises sheer above the sea, and everywhere has so abrupt a declivity that the streams which flow seaward are all short and swift.

[1] The descent from the southern range to the high plateaux of Castile is more gradual, and several large rivers, notably the Ebro, rise here and flow to the south or west.

Many peaks are over 6,000 feet (1,800 m) high, but the greatest altitudes are attained in the central ridges on the borders of León, Asturias, Palencia and Cantabria.

A conspicuous feature of the chain, as of the adjacent tableland, is the number of its parameras, isolated plateaus shut in by lofty mountains or even by precipitous walls of rock.

[5] The Basque Mountains at the eastern end of the system, with very eroded Mesozoic folds and ranges of moderate height: The Cantabrian montane woodlands are dominated by deciduous trees and evergreen conifers, primarily of the Fagales (beeches, hazels, oaks, walnuts) order, including European beech (Fagus sylvatica), English, holm and Pyrenean oak (Quercus robur, Q. ilex, Q. pyrenaica), as well as numerous junipers, pines and yews, among other species.

[10] A combination of overhunting, human encroachment and loss of suitable wild habitats have led to the brown bear's gradual decline on the Iberian Peninsula.

Some of the sites are included in the European Union's Natura 2000 network and Special Protection Areas for the Conservation of Wild Birds.