The reserve, on the sunny side of middle Valtellina, in an area between 700 and 800 meters above sea level called "Il Prato" in Postalesio, consists of a small moraine deposit with debris of different sizes. Here the phenomenon of the "Pyramids of earth" is manifested, it arises from the erosive action exerted by rainwater that, falling, erodes and crumbles the soil made up of debris, leaving intact only the compact boulders. This is the origin of these columns surmounted by boulders of different sizes. The process is still active today. Alongside the existing ones, some formations can be seen at the initial stage. The existence of small valleys dug between the pyramids creates a particular microclimate that allows the development of a dense forest with the simultaneous presence of species of cold climates, including larch, spruce, silver fir, scots pine; alongside species that prefer warmer climates.
In addition to the 7 main Pyramids, it is possible to observe new Pyramids in the formation phase and moraine deposits that lead to the formation of other Pyramids. It is also possible to see numerous boulders emerging from the ground, which, in the near future, will be able to act as "hat" of new Pyramids.