Editing Geography of Saudi Arabia (section)

=== Great deserts ===
[[File:JUBBAH 16.jpg|thumb|Highway crossing the Nafud desert]]
Three great deserts isolate the great plateau area Najd of Saudi Arabia from the north, east, and south, as the Red Sea escarpment does from the west. In the north, the [[An Nafud]]—sometimes called the Great Nafud because An Nafud is the term for desert—covers about 55,000 square kilometers at an elevation of about 1,000 meters. Longitudinal dunes—scores of kilometers in length and as much as 90 meters high and separated by valleys as much as 16 kilometers wide—characterize the An Nafud. Iron oxide gives the sand a red tint, particularly when the sun is low. Within the area are several watering places, and winter rains bring up short-lived succulent grasses that permit nomadic herding during the winter and spring.

Stretching more than 125 kilometers south from the An Nafud in a narrow arc is the [[Ad-Dahna Desert]], a narrow band of sand mountains also called the river of sand. Like the An Nafud, its sand tends to be reddish, particularly in the north, where it shares with the An Nafud the longitudinal structure of sand dunes. The Ad Dahna furnishes the Bedouin with winter and spring pasture, although water is scarcer than in the An Nafud.

The southern portion of the Ad Dahna curves westward following the arc of the Jabal Tuwayq. At its southern end, it merges with the [[Rub' al Khali]], one of the truly forbidding sand deserts in the world and, until the 1950s, one of the least explored. The topography of this huge area, covering more than 550,000 square kilometers, is varied. In the west, the elevation is about 600 meters, and the sand is fine and soft; in the east, the elevation drops to about 180 meters, and much of the surface is covered by relatively stable sand sheets and salt flats. In places, particularly in the east, longitudinal sand dunes prevail; elsewhere sand mountains as much as 300 meters in height form complex patterns. Most of the area is totally waterless and uninhabited except for the few wandering Bedouin tribes.