The Ru des Hauldres is a river which joins the Seine near the Étiolles site. Its drainage basin covers the majority of the plateau and was an important source of sediments during the Tardiglacial. The silt covering Magdalenian remains at Étiolles comes from the erosion of the plateau and alluvial deposits from the Seine.

DAO © Yann Le Jeune
Drainage basin of the Ru des Hauldres. Magdalenian camp at Étiolles. Essonne