It is also called the Lys Valley, from the name of the stream that originates from the large glacier with the same name located on the Monte Rosa massif. It develops in the Aosta Valley territory from north to south, between the Ayas Valley and Valsesia, in Piedmont.
The main Walser proofs are found in the territory of the municipalities of Gressoney-Saint-Jean and Gressoney-La-Trinité, in the Niel Valley (Gaby) and in the San Grato Valley (Issime).