From the geological point of view the Alpi Biellesi are composed by an alpine zone in the strict sense of the word and a prealpine zone, divided by the Insubric line (locally named Linea del Canavese). This important geologic fault, which forms the border between the Adriatic plate and the European plate, crosses Biellese from SW to NE through Bocchetto di Sessera and Bocchetta della Boscarola passes. Thus hills and mountains (i.e. Monte Barone) located south-east of the line can be considered part of southern Apulian foreland while most part of the range, located NW of the line, geologically belongs to the crystalline zone of the Alps.