The last geological events that affected Mount Caslano were those of the Quaternary period (from 2.6 million years ago to today). In the Pleistocene, the earlier of the two epochs of this period ended 11›700 years ago, the climate was marked by the alternation of cold and hot phases that determined the advance and withdrawal of the Alpine glaciers on several occasions. During the cold phases, the glacial tongues invaded the valleys, descending to the edge of the Po Valley.
In this way, Monte Caslano was repeatedly covered by a branch of the Ticino Glacier, which reached this region via the Monte Ceneri Pass, and even by a branch of the Adda Glacier, which came from the region of Porlezza.
Between 27,000 and 23,000 years ago (phase known as the Last Glacial Maximum), Monte Caslano was completely covered by glaciers for the last time.
The morainic deposits and erratic boulders which were abandoned during the subsequent phase of glacial retreat, are evidence of this period.
Moraines are composed of fragments of rocks, mixed with sand and clay, mostly from the Sopraceneri half of the region. They cover in particular the northern slope and the summit of the mountain. The erratic boulders are blocks dragged by the ice and abandoned when it melted: they stand out today for the different substrate on which they rest. They have long represented a valuable building material, as they often consist of hard crystalline rocks of Sopraceneri, including a granitic gneiss widespread in Riviera, lower Leventina, Val di Blenio and lower Mesolcina. For this reason, they were widely used in the past to make columns and lintels, steps or other artefacts.
