the red sea hills are composed of the exposed neoproterozoic volcano-sedimentary rock of the arabian-nubian shield. although the rock itself is 550–900 million years old, the mountains were created by uplift when the red sea itself was formed in the oligocene, only some 23–34 million years ago. the red sea hills are thus part of the same formation as the sarawat mountains of saudi arabia and the mountains of the sinai peninsula. the red sea hills rise almost to today, but in the past were much higher. the oligocene uplift caused the rejuvenation of their streams and the increased erosion removed most of the limestone and sandstone to expose the basement layer.