‘Foces’ are deep incisions in rock caused by river systems. In the mountain region of Navarra, the rivers basically run North-South, while in its mountain ranges and chains, they run East-West. ‘Foces’ are formed where the two meet. Water and rock, particularly alternating soft and hard layers, together with time (the process takes millions of years), are the essential elements for the creation of a ‘foz’.

The word ‘foz’ comes from the Latin word “faux, fauces”: throat. In most of Spain, such formations are known as ‘hoces’, but other words, such as ‘gargantas’, ‘cañones’, and ‘desfiladeros’, are also used. ‘Foz’ is not the only word in Navarra used to describe these geological formations; the Basque language uses the words “potxe” (a narrow area of land between two high points), “atea” (doorway or pass between mountains, but also gorge or narrowing of a valley) and “txintxurris” (ravines).

Such formations are abundant in Navarra, particularly in the pre-Pyrenees. Some of the best-known examples are the Foz de Lumbier and the Foz de Arbayún, both in the pre-Pyrenean district of the Community of Navarra.
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