The valleys that give access to the Pyrenean mountains, in which the pine has been exploited since ancient times, were formed around the rivers that served as a means of communication and extraction of the wood, which represented the wealth for the community settled in them.

This path starts at the Laza pass, between the Roncal and Salazar valleys, and reaches the hermitage of the Virgen del Yugo, in Arguedas, in the middle of the Bardena, and coincides with the GR-13 long-distance route.

The extensive basin between the Ebro depression and the Pyrenees, composed of deposits from the secondary and tertiary periods of marine origin, has in the mountains that make up the Sierra de Leyre an important and relevant geographical and structural feature.

The range runs in an east–west direction, and consists of two parallel alignments, in whose central depression Bigüezal and Castillonuevo are located; in its northern foothills it forms the Sierra de Illón, with its maximum height in the Borreguil (1420 m.a.s.l.

Three rivers, the Esca, the Salazar and the Irati, cross the mountain chains forming very abrupt valleys, which are known by the name of foz, and which from a landscape and natural point of view are of great importance.

Morphologically, the Foz de Arbayún and the cliff that opens on the Berdún channel are very relevant, as well as the abrupt end of the mountain range on the south side.

This spectacular cut that the Salazar River makes in the rock has a length of 6 km and a maximum depth of 385 m. In 1975, ICONA included it in the National Inventory of Outstanding Landscapes.

and among the mammals the wild boar, fox, badger, fuina, wild cat, genet and weasel, and more scarce but present, otters and roe deer.With just over a kilometer long and a 120-meter drop from the Irati River, this steep pass of vertical walls contains one of the most important nesting areas in Navarra, protected as a Natural Reserve.

On the shelves that form on the walls of the foces inhabit some relevant species because of their endemic character or their extreme biogeographic position, some of them are Saxifraga longifolia, Sarcocapnos enneaphylla, Saponaria glutinosa and Petrocoptis hispanica.

In the range itself is located the Monastery of Leyre that has the most relevant construction of the Navarrese Romanesque and royal pantheon of the kings of the Pamplona Najera kingdom, nearby, already in Zaragoza, is the monastery of San Juan de la Peña also Romanesque and royal pantheon of the kings of Aragon, within its walls was kept the Holy Grail for a long time, according to legend.

One of the most typical routes in this range is the ascent to Mount Castellar, 1286 m high, starting from the monastery of Leyre and following the Cañada Real de los Roncaleses (GR-13).

Shortly after starting the route, a detour to the left takes us to the Fuente de San Virila.

Following the gully, in a strong slope, we arrive at the Portillo de La Cerrada, also called col of Leyre.