The geological substratum of the gullies area is characterized by the presence of a calcareous basement on which various clay layers mixed with sand and limestone material have been superimposed over time, from the union of which originates an "impasto" easily crumbling. Gullies are an erosive phenomenon that is a consequence, on the one hand, of the aforementioned characteristics of the soil and, on the other hand, of the particular climatic conditions of this area: during the dry summers in these areas, the sun causes the soil to dry out (in fact, gullies are formed mainly on south-facing slopes), which favors the formation of fissures, into which, in the rainy winter months, meteoric water penetrates, causing the ground to break up. Their formation is also affected by the extensive wild logging implemented in these areas between the 1800s and early 1900s. Gullies take on very diverse forms: gully fronts, characterized by a concave shape and marked by innumerable rivulets; mamellonary gullies, small rounded reliefs placed one on top of the other; biancane, small isolated rounded reliefs, which take their name from the presence in summer of a white patina that covers their surface, a consequence of saline exudation; gully ditches, placed next to each other and divided by thin ridges; and knife-edge gullies. Despite the fact that the phenomenon of gullies causes the acceleration of the processes of desertification of the territory and renders vast lands sterile and unusable from an agricultural point of view, the peculiarity and singularity of the phenomenon itself induces the pursuit of its environmental and touristic valorization. Much space, moreover, is found for gullies in literature. Carlo Levi in "Christ è stopped at Eboli" soì describes them: "... and all around other white clay without trees and without grass, dug by the waters in holes, in cones, sores of malignant appearance, like a lunar landscape ..." and again " ... and on all sides there were nothing but precipices of white clay, on which the houses stood as if released into the air". Albino Pierro, a poet from Tursi, dedicates a poem "'A jaramme" to the ravines, and calls his land "a terre de iaramme", the land of ravines, precisely by virtù of the force of the ravines in defining the structure of the landscape of these places.
