The Buëch starts several kilometres to the east of "col de la Croix-Haute", a mountain pass in the western side of the "Massif du Dévoluy" mountains, in the "commune" of Lus-la-Croix-Haute, Drôme department, at an elevation of about . It then flows to the southwest and gets into the Hautes-Alpes department and then flows to the south.