From south-east to north-west there are lithologies belongings to the Austroalpine and upper Pennidic and lower Pennidic multinappes system.
The structural asset of the Austroalpine and upper Pennidic units is verticalized (Loro-Vogogna/Domodossola) so the single units outcrops with low power.
The Austroalpine in the Ossola region is represented by the "Sesia-Lanzo -SL" area, formed by paragneiss, ortogneiss and metabasitics. Some kinds of beolas (the Vogogna beolas) belong to this unit lithologies.
Between the Austroalpine and the Pennidic nappes there is the Piedmont Area, formed by calcescists and green stones, which in the Ossola Valley outcrops in a weak way while it outcrops better in the Aosta Valley.