Trio of 'black mesas' leftover from Paleozoic era spawn rare sand dunes in the Sahara — Earth from space

Trio of 'black mesas' leftover from Paleozoic era spawn rare sand dunes in the Sahara — Earth from space

A 2023 astronaut photo shows three dark hills, or mesas, towering above part of the Sahara desert in southern Mauritania. The structures are remnants of a single Paleozoic era formation, and have helped to create a series of striking sand dunes.