Besides being considered by some the westernmost tip of the Pyrenees (rivalling with the coastal mountain Jaizkibel), it stands out as a distinctive range of rocky prominences and gullies, otherwise uncommon. The conspicuous formations of Aiako Harria consist of a Paleozoic massif with some of the oldest materials cropping out currently in the Basque Country. Later orogeny pushed a mass of igneous rocks to the surface, so metamorphosing the superficial Paleozoic materials as it tore its way out of them, which yielded the present day granitic landscape.