The Arona area is of great interest for its geology, and the red porphyry paving stones used all over the town are an example.

If you walk along the road from San Carlo hill to the lake you can see a number of rocks of volcanic origin, as well as a large quantity of dolomite, a sedimentary rock formed of carbonate and magnesium, evidence that this area was once covered by the sea. The rock still bears the signs of abundant deposits of skeletons of calcareous algae.

The dolomite of Arona characterizes the whole landscape; all of the Rocca of Arona is composed of it, and it has been widely used in the town as a material for building, as a facing stone and for ornamentation. In some parts of Arona you can see the karstic effects resulting when the dolomite dissolves in water, producing curious underground networks of channels and caves; the swallow-hole in the locality known as “Cascina Vescovo” is an example.