Grand Erg Oriental follow the wind's direction. There are other types of dunes, as well as "complex" dunes. Saharan winds are also known to clear an area of sand altogether, leaving bare rock (hamada) or gravel (reg). The "Grand Erg Oriental" is accessible overland by an Algerian road, which goes south from Constantine. It passes through the Aurès mountains, then salt lakes by the city of Biskra. Next the road skirts the western edge of the erg. After about 500 km. in all, it reaches the ancient oasis of Ourgla [Wargla]. Since late antiquity Wargla was a stop for the Saharan trade, being
Erg Iguidi Erg Iguidi The Erg Iguidi (), is a large erg in the area of Tindouf in southwestern Algeria extending into northern Mali and Mauritania. The Erg Iguidi is a sandy desert with a clear pattern of narrow linear dunes stretching for a length of 400 km. Part of the greater Sahara, it is located in its northwestern region and is characterized by Harmattan withering winds. The highest point is 540 m. Compared to the neighboring Erg Chech to the south, this erg is relatively humid. Groundwater is especially abundant towards the north-eastern edge of the Erg Iguidi. There are patches