Richat Structure in the Sahara Desert of Mauritania21.1N 11.4W
This pattern of concentric circles in the Saharan Desert near Ouadane, in Mauritania, is known as the Richat Structure. Due to its bullseye-like shape, it was originally believed to be a crater from a meteorite impact. However, scientists now believe that it is a circular anticline whose crest has been eroded away.
The structure is at least 40 km in diameter. Erosion has created circular cuestas represented by three nested rings dipping outward from the structure. The center of the structure consists of a limestone-dolomite shelf that encloses a kilometer-scale siliceous breccia and is intruded by basaltic ring dikes, kimberlitic intrusions, and alkaline volcanic rocks.