The whole area through which this track follows is underlain by Gerês granite (biotitic granite, sometimes with a rose colour, porphyritic texture, coarse grain on the margins then transforming into medium to coarse grain in the massive core and with some phenocrysts of potassic feldspar). As we walk along the road one can notice a large quantity of sand deposited on the side. These sediments are known as “arena”, granitic sand or gravel, resulting in the arenitisation phenomenon, provoked by the disaggregation to which the rock is subjected when water penetrates and flows through on its fractures. The material resulting from arenitisation is used by local people as gravel for a great diversity of purposes, including construction work and paving. The place from where the gravel is extracted is known as the “saibreira” (gravel-pit).