This geological monument is made up of a central volcanic (neck) of alkaline basaltic lava (hawaiite) characterized by a peculiar columnar cracking. Mount Cepera (167 meters above sea level), the name of the volcanic relief, highlights this particular volcanic cooling structure through an old quarry front used for building material and bricks. The basaltic eruption is due to the last magmatic cycle that affected Sardinia between the Middle Miocene and the Upper Pleistocene, related to the opening up of the Tyrrhenian Sea. The quarry front has enabled to better highlight the cracking typology and the prism disposition that, compared to other similar Sardinian areas, is clearer and more distinct. During the cooling of a lava flow of a certain thickness, joints and the fractures are formed, and the fractures take an amazing prismatic-columnar shape with a hexagonal or squared base.