Abstract. The 50 to 100 metre deep canyon of the Sarine River that develops north of the prealpine front in the Molasse Plateau is classically attributed to postglacial erosion. However, the discovery of a Mesolithic archaeological site (~ 8600 years cal. BP), located at the bottom of the gorge five metres above the actual river bed, has evident implications for the canyons morphogenesis. This new chronological datum indicates that most of the canyon was already formed 8600 years ago, and that only five metres of Molasse have eroded since that time. This implies a dramatically high erosion rate during Late Glacial to early Holocene times 0.9 to 1.48 cm/ year) and, consequently, a very low erosion rate since the Atlantic period approximately 0.06 cm/ year). These new archaeological and geological findings offer exciting perspectives for Quaternary research.