The so-called Richat structure in Mauritania, Africa, not a meteor crater but a geological structure caused by the erosion of an ancient volcano.
The 39km wide form was made by the erosion of layers of rock which domed upward. The depression or pit in which the domed rock rings sit is 100m deeper than the surrounding plateau area (darker coloured rock).
The rock layers may be several hundred million years old. Different rates of erosion have created a series of concentric ridges stepping down from the outside. It is surrounded by fields of sand which are visibly encroaching into the southern part of the structure. Small dry lakes or playas (whitish-grey colour) are discernible to the east of the centre part of the bullseye.