Yet such dry, anciently-made river beds, lying seemingly useless beneath the desert sands, can preserve the infrequent rain water, by carrying it off underground and so rescue the moisture from an otherwise "intense and almost instantaneous" evaporation.

[3][4][5] A buried river bed "not only serves in certain cases to carry into the heart of the desert the waters of distant rains which have fallen outside the desert domain, but in it the waters of the local storms are concentrated and carried swiftly to the alluvial basins where they are imbibed by the lighter earth and form lasting reserves within its depths.

The Grand Erg Oriental "appears to have been pushed forward on the east and southeast slopes" toward Ghadames at the Libyan border.

Seif dunes generally form long rows whose parallel ridge lines follow the wind's direction.

Saharan winds are also known to clear an area of sand altogether, leaving bare rock (hamada) or gravel (reg).

Since late antiquity Wargla was a stop for the Saharan trade, being situated along a caravan route of several thousand kilometers, stretching from the Mediterranean to the Sahel.

Wargla was the capital of late medieval M'zab, an Ibadi political entity descended from the earlier Rustamid polity.

North of Wargla [Ouargla] lies Touggourt [Tuggurt, Taghit] (pop: 153,000), where date palms are grown commercially.

Until recently Hassi Messaoud was a small Saharan village, but has grown substantially on account of the local discovery of oil in 1956.

Nearby, within the accepted boundaries of the Grand Erg Oriental, the landscape is described as being "practically free from [sand] dunes" evidently due to strong, persistent winds.

[23][24][25] Along the north rim of the Grand Erg Oriental, both the physical ecology and the human culture surviving there since ancient times are said to form a continuum.

[26] It is a low-lying area of chotts (salt pans), and occasional oases, where exists intensive cultivation of date palms in the tens of thousands.

[27][28] Between Biskra and the Djerid, but a little to the south, lies El Oued, a mid-sized Algerian city (pop: 139,000), graced with domes and arches of Saharan architecture.

[31] South of the Tunisian sea port of Gabès, in the vicinity of the Grand Erg's northeast edge, there are a number of Berber villages, among them Tataouine.

[32] From here a bleak Tunisian paved road leads south along the Libyan border, by sand dunes of the Grand Erg's eastern limits, terminating at Borj El Khadra, an oasis, near Ghadames.