Cantabria is a mountainous and coastal region, with important natural resources. It has two distinct areas which are well differentiated morphologically:

Coast. A coastal strip of low, wide and gently rolling valleys some 10 kilometres in width, the altitude of which does not rise above 500 metres, and which meets the ocean in a line of abrupt cliffs broken by river estuaries, forming rias and beaches. Santander Bay is the most prominent indentation in the coastline. To the south, the coastal strip rises to meet the mountains.

Mountains. This is a long barrier made up of abruptly rising mountains parallel to the sea, which are part of the Cantabrian Mountains. The mountains are mostly made of limestone with karst topography, and occupy most of Cantabria’s area. They form deep valleys running north–south. The torrential rivers are short, fast flowing and of great eroding power, so the slopes are steep. The valleys define different natural regions, delimited physically by the intervening mountain ranges: Liébana, Saja-Nansa, Besaya, Pas-Pisueña, Miera, Asón-Gándara, Campoo. To the ‘mountain’ region belongs the Escudo Range, a mountain range of 600 to 1,000 metres (2,000 to 3,300 ft) high that covers 15 or 20 km (9.3 or 12.4 mi) in a parallel line to the coast in the West part of Cantabria.

Towards the south are higher mountains, the tops of which form the watershed between the drainage basins of the Rivers Ebro, Duero and the rivers that flow into the Bay of Biscay. These peaks generally exceed 1,500 m (4,900 ft) from the Pass of San Glorio in the west to the Pass of Los Tornos in the eastern part: Peña Labra, Castro Valnera and the mountain passes of Sejos, El Escudo and La Sía. The great limestone masses of Picos de Europa also stand out in the southwest of the region: most of their summits exceed 2,500 m (8,200 ft), and their topography is shaped by the former presence of glaciers.