The structure of the rock itself and the complex architecture of the western Alps range situated along the structural section of Ossola-Verbano, allows for the reconstruction of principal geological events that took place in the Alps over millions of years, from their Palaeozoic period orogenesis up to the development of the Alps; the latter action began with the Mesozoic ocean (Tetide) and its subsequent closure to the point of collision, an action that is still in progress today, between the African and European continents. It is with good reason that the Ossola region played a decisive role, from the end of the 1800's to the beginning of the 1900's, in the development of modern geological thought and the confirmation of migrational structure theories: it was here, rather than from the entire western Alps sector, that the first models for overthrust mass ranges were created, and the first methodological principles for kinematics analysis were introduced along with the first reconstructions of paleogeographic environments. In more recent times, the V.C.O. territories have become natural laboratories for further study in the earth sciences, from tectonic plate applications to the Alpine ranges, to the development of highly advanced geodynamics and kinematics reconstruction based on integrative interpretations of new geological, geophysical, petrologic, geo-chemical and chemo-physical data.

It is not easy, however, to discuss the geology of the area under examination given the complex layering processes that have happened over time. Strictly speaking, Hercynian history begins approximately 400 millions of years ago (from the Devonian period of the Palaeozoic era) through collisional orogenesis, stratum tectonics, crustal thickening and regional multi-phase metamorphisis, from its original conditions of relatively high pressure (cyanite residue) and moving towards a lower pressure (andalusite). In the late Palaeozoic era, (some 300 to 250 million years ago) a complex magmatic activity took place, with volcanic, sub-volcanic and plutonic manifestations. This activity extended from the Upper Carboniferous period to the Permian or was exclusively Permian, having an affinity to calc-alkaline; the latter is the case with Baveno-Mottarone-Montorfano granite, or Lake Granites, embedded in a pre-existing crystaline deposit (Lake Schists), which underwent metamorphosis and formed during the Hercynian cycle (figure 2). Like the schists in which they are embedded, the gra-nites no longer underwent metamorphosis or successive bending deformation, having maintained, during the higher temperatures of thermal deformation, a surface structural level, a non-axial position and non-metamorphic position in the Alpine range.

Beginning from the Upper Carboniferous period, final erosion and rising processes of the Palaeozoic range produced widespread surface erosion. The following extension of the Permian/Mesozoic crust and the formation of a divergent continental edge brought about the opening up of the Liguria-Piedmont ocean (Jurassic palaeography) until arriving the development of the current Alpine range through the evolution in the Cretaceous period (130 million years ago) of the converging compressive crust of the Europe/microplate Adria.