The famous ancient rock art in the Cave of the Swimmers at the foot of the Gilf Kebir plateau (which is the size of Puerto Rico in extreme southeastern Libya) dates to the Ice Age when rainfall abounded where now is the Sahara, when the Abu Ballas trail from the Dakhla oasis (then a lake) in west central Egypt to the Gilf Kebir was traversed by donkeys, not camels which were not much used until the Ice Age had ended. Consult the work of Carlo Bergmann, great discoveries such as also Djedefre’s Water Mountain, which was a mining site for pigments (for painting the pyramids) about fifty miles to west of the Dakhla basin along the Abu Ballas trail.
