The Montagnayes gorge, in the commune of Bionaz, stretches from 1573 m at the bottom of the valley to 3321 m at Becca-des-Arbyères. Situated on the left-hand side of the Buthier stream, the valley offers visitors typical sub-Alpine and Alpine landscapes, with mixed forests of spruce and larch, which gradually open up towards the crests to make way for Alpine pastures and meadows, with rare species of flora in the whole of the Alps and the region.
Chamois, foxes, badgers, martens, beech martens, golden eagles, dwarf owls, choughs, amphibians, reptiles and a world of diurnal butterflies populate this rich and still unspoilt natural environment.