The Ossola Valley, wedged in Swiss territory, between Valais and Ticino, represents the north extreme of Piedmont, in Verbano-Cusio-Ossola province. It is crossed by the Toce river and is assembled of numerous lateral valleys, including the Anzasca Valley, the Formazza Valley, the Antigorio Valley and the Strona Valley.
The Walser settled in the Anzasca Valley arriving from Saas-Fee, through the Monte Moro Pass, to Macugnaga, where the imposing east face of Monte Rosa dominates.
In the upper Toce Valley the Walser arrived from the Gries pass, founding first the numerous hamlets of Formazza Valley and then those of Val Antigorio, including Salecchio, in the municipality of Premia, and the now disappeared village of Agaro, in the territory of the municipality of Croveo.
Descending towards the lower part of the valley, almost on the shores of Lake Maggiore, they founded the town of Ornavasso.