The morphogenetic processes that gave rise to the basin of Leonessa date back to the Lower and Middle Pleistocene (1.8 million years ago), thanks to the discovery of some mammalians (remains of elephants) and shellfish of fresh water of Galeriano within fluvial-lake sediments that characterized the area. Then the basin was drained by an outflow due to a new tectonic phase, which originated a morphology of the landscape not much different from today's one. It is therefore clear that the territory of Monteleone di Spoleto is characterized by a continuous geological and geo-morphological evolution.

The history of these mountains began about 200 million years ago, in the Jurassic Period. It is interesting to emphasize that in the territory of Monteleone di Spoleto there are the limestone rocks of the Stratification of Umbria-Marche, which was formed in the marine environment and sometimes rich in fossils (ammonites, gastropods, bivalves, crinoids, foraminifera, etc.) ranging from the Lower Jurassic (about 200 million years ago) until the Paleogene period (10 million years ago). The fossil remains that are found in these rocks allow us to reconstruct the period in which they were formed. From this, we know that about 200 million years ago, also in this area there was an environment similar to that of the current Bahamas, with coral islands, warm and shallow sea. Subsequently the seabed became deeper though rather irregular with ups and downs structures, which were soon smoothed out by the limestone sediments that were deposited on the seabed.