[user070223]

Indeed, one great path to finding those lost civilizations is to follow river vallies, Atlas pro[0] says there is no consensus on past rivers/bodies of water as evident by different maps of the region, but one can follow (underwater) river sediment which were deposited to the sea. During oil search such area was found in Cap Timiris, Mauritiania. Satelite radar image of the area from 2015 did reveal those rivers beds, Tamanrasset River seems to be the biggest, with a big drainage basin. Trees and shrubs indeed grow there.

[0] https://www.youtube.com/watch?v=r-dZj1ZdRtY