Galicia is traversed by mountain ranges, sometimes regarded as a continuation of the Cantabrian chain; and its surface is further broken in the east by the westernmost ridges of that system, which, running in a south-westerly direction, rise above the basin of the Mino.
The Ebro rises at Fuentibre, a hamlet among the Cantabrian Mountains, in the province of Santander; at Reinosa, 4 m.
The surface of the country is for the most part very mountainous, being traversed towards the south by the great Cantabrian chain; but at the same time it is diversified with numerous narrow valleys and small plains.
Asturias consists of a portion of the northern slope of the Cantabrian Mountains,and is covered in all directions with offshoots from the main chain, by which it is almost completely shut in on the south.
The existing frontier is marked on the north by the Cantabrian Mountains; on the east by the Sierra de la Demanda with its offshoots, and by the Serrania de Cuenca; on the south by the Sierra Morena; and on the west by various minor ranges which link together the three more or less parallel chains of the Sierra de Gredos, Sierra de Guadalupe and Sierra Morena.