Why are parts of the Atlas Mountains in Morocco flat?
Once the sediments (mainly silt and sand) have been deposited as layers in an ocean, when the sea level was much higher. Thus, each layer is very homogeneous in its texture, hardness and stability against weathering and erosion. Therefore vertical forces of erosion have a uniform effect on the entire surface and the ridge remains flat when there is no deformation due to tectonic strain. But lateral erosion has different effects on the different hard layers and so you see ribs on the mountains flanks. So it is mainly due to the layer homogenity and due to the absence of tectonic deformation that you see in the background.