In the western part of the Gilf Kebir and its foothills at the Libyan side is observe widespread conspicuous red discolored areas on the satellite image. Locally it should be noted that these surfaces are covered with hardened ferruginous sandstone plates on the plateau or detritus on alluvial plains. In the geological profiles of the hills and mountains in this region is to observe a several changes of these thin red layers with white sandstones.
This change between red and white sandstones is secondary caused by the influence of water. During a time, that we do not know, it came by massive irrigation of the sandstones to a separation in the color. In the white sandstone the iron oxides were washed out. The red sandstone layers can be thought as a drain, in which the transported iron oxide was not soluble deposited again.
The red and white sandstones occur in principle everywhere, regardless of its stratigraphic position, but probably regionally dependent.
It is striking that the Gilf Kebir plateau, with the compact Devonian strata, is hardly or not affected by the phenomenon of leaching. Except the Abu Ras passage east of Jabal Asa, and also near Wadi Sura, in the lower parts of the Ordovician sandstones, are leachings to observe.
The Abu Ras passage, in which the most impressive leachings are to seen in sandstones of Ordovician age, like the entire western Gilf Kebir with its Carboniferous layers (Wadi Talh in the broadest sense) was in the past located in a major drainage system.
 

Another specialty are red clayey layers within Carboniferous strata in the Wadi Talh (western plateau along the Wadi Abdel Malik) and in the western foreland at the Libyan side, which are also partially exposed. These deposits are not formed secondarily. They document marine floodings in the Carboniferous period.