The granitic deposit of the upper Val Ferret was shown in 1980 to result from a large September 1717 rock avalanche. A huge volume of rock and ice travelled onto the Triolet Glacier>7 km downvalley. Boulder accumulations and irregular ridges spread out over a distance of 2 km on the valley floor terminate with an arcuate front. A 2009 reconstruction with radiocarbon dating proposed a smaller lateral extension of the landslide on the valley floor preserving Lateglacial moraines, but cosmogenic exposure dating questions it. Consistency of 10Be dates suggests that the deposit results from the 1717 rock avalanche, with a rock volume>10×106 m3, and a likely similar ice volume. The importance of rock avalanches has to be emphasised to help to prevent risk in inhabitated valleys. Even for the recent period, the contribution of cosmogenic exposure dating to geomorphological analysis of complex landform assemblages is valuable.