The Verbano Cusio Ossola Province is located in the central western Alps and has had great importance for geological studies about the Alps since the last century.
The Alps are a double-vergent chain : an European one and an African one, the southern Alps divided by an important tectonic line named Lineamento Periadriatico or Insubric Line.
This is called Linea del Canavese (Ca) and it crosses the Ossola Valley, it is located in the surroundings of the municipality of Loro.

The geological peculiarity of this area is the possibility to see the lithologies and the deepest structures of the Alps chain. Ossola allow to see the overlap of nappes piled during the Mesozoic era and the Third era.
This is possible thanks to the regional inclination of the nappes building toward SSE, to tectonical processes and to the differential heaving, which is maximum in the Formazza Valley, heart of the Ossola tectonic window.

From a geological point of view in the VCO area it is possible to classify two great structural domains from south-east toward north-west:

• The basement of the Southern Alps (Subalpino) in the south-eastern area
  
  
• l’The Alps napes building or "European vergent orogenic system" in the north-western area, it lies to the North of the Linea del Canavese.

The Southern Alps basement is composed by the Series of the Lakes, in the south-east area, a middle continental crust portion and Ivrea-Verbano Area, a deep continental crust portion.

The Series of the lakes is formed by pre-alpine metamorphic rocks, in anphibolitic fancies, composed by pelitic-psammitic and metagranitoids of the Ordovician age (470 Ma).
The series is intruded by plutonic bodies of the late Variscan age (280 Ma) to which belongs granodioritic granitic masses called Granites of the Lakes (Baveno-Mottarone, Montorfano, Alzo, Roccapietra and
Quarna).

The Ivrea-Verbano Area is formed by pre-alpine metamorphic rocks in anphibolitic fancies of high granulitical temperature. They have a politic-psammitic composition with lenses of maphic and ultramaphic rocks and marbles.
The structural asset of this area is subvertical as a result of some alpine age tectonic events. The so called "Nero di Anzola" (Black of Anzola), the Candoglia and Ornavasso marbles belong to this tectonic unit.