The mountainous relief is covered by an extensive forest formation that is of great naturalistic and landscape interest, preserving numerous botanical and faunistic realities. On a geological level Mount Duro is part of a wider outcrop of "flysch" which includes, to the east, the reliefs of Mount Pilastro and Mount Lusino. The formation, which dates back to the final part of the Upper Cretaceous (Senoniano) and probably reaches the beginning of the Tertiary period (Paleocene inf.) consists of well stratified sequences of limestones, often with arenaceous base, marls and argillites. The reduced resistance to atmospheric agents of marls and clays has given rise in this sector to a significant phenomenon of selective erosion, with the formation of the so-called "walls of the devil" (the residual part of the layers, of calcareous-arenaceous nature), clearly visible along the SS 63 at the Bocco. Of some interest is the discovery in the upper part of the formation of the "paesina stone", once also called "ruiniform limestone", since it simulates the appearance of a ruined country, sometimes in a truly suggestive way.