Around twenty archaeological sites in upper Nubia give evidence for the existence of the Qadan culture's grain-grinding culture. Its makers also practiced wild grain harvesting along the Nile during the beginning of the Sahaba Daru Nile phase, when desiccation in the Sahara caused residents of the Libyan oases to retreat into the Nile valley.[15] Among the Qadan culture sites is the Jebel Sahaba cemetery, which has been dated to the Mesolithic.[16]