Hundreds of meters of turquoise sea and rounded grains of fine quartz, similar to rice grains, declined in a suggestive escalation of colors, from green to white, passing through the delicate pink. Is Arutas is one of the jewels of the Sinis Peninsula Protected Marine Area – Mal di Ventre Island, in the Cabras area, just over ten kilometers north of the town. It consists of almost completely siliceous grains the size of a grain of rice, approximately. Other colors of the beans bring to mind granite or gneissitic environments, but looking around there is no trace of these lithologies; not even a diving in the vicinity would give significant results, in fact, for the entire length of the coast and in the whole area there are no granites or other paleozoic rocks, except in the nearby island of Mal di Ventre almost completely made up of a granite whitish gray porphyroid. Said granite contains large white feldspar crystals and often long plagues rich in biotite, this system is crossed by strands and clusters of haplites, lamprofiri and basic differentiations.
The only significant variation consists of some thin plaque of a sandy, calcareous arenaceous-calcareous deposit with sandy, yellowish brown or a little reddish earth in which rabbits once had their burrows, this is the characteristic for which the the name of Is Arutas has been attributed which in Sardinian means caves, they are very small flaps of the Tyrrhenian bench, with very rare fragments of marine shells, covered with little degraded wind sand and encrusted with calcium carbonate, for thicknesses usually lower one meter.
From what has been said, the connection between the breakdown of the granite lithologies of the island in question and the coastal sandy deposits of the island itself and the area of Is Arutas is clear.
At Punta Is Arutas, Quaternary fossils of great interest are found such as acantocardia, glycimers, patellas, etc.