At the end of the Cretaceous period, the sea that from the Triassic period had been the cradle of the rocks around Lugano. closed as a result of compression between Africa and Europe. The sediments deposited on its bottom began to deform, prelude to the formation of a new mountain range: the Alps. As a result of this the rocks of Monte Caslano appear to us today in layers strongly inclined southwards, sometimes vertically. These movements are also responsible for the formation of the Monte Caslano fault, an almost vertical surface, oriented east-west, that cuts the dolomite and divides the mountain into two blocks, one having slipped from the other. At this point, the fault plane appears exposed, forming steep unstable walls and extensive deposits of rock debris at their feet.
On these deposits and in the abandoned caves on the southern and western sides of the mountain, a pioneer vegetation develops, characterised by plants capable of colonising apparently inhospitable substrates, formed by coarse crushed stone, a small fine mineral portion and an almost total absence of humus. In these screes scattered trees can settle: the most widespread species are the mountain ash, the black hornbeam, the scots pine and the black pine, a naturalised exotic species. They are accompanied by some heat-loving (thermophilic) and drought-resistant shrubs, such as the snowy mespilus, the St Lucie cherry and the Avignon berry, a species quite rare in Ticino. The herbaceous layer is poorly developed, deficient, composed of pioneer thermophilic species that colonise the debris of calcareous strata, such as the elegant rosemary willowherb, the mountain germander and the dark red helleborine.
In the long term, this pioneer growth is likely to be replaced by black hornbeam shrubland.
