Editing Geography of Saudi Arabia (section)

===Hejaz===

[[Image:Saudi-desert.gif|thumb|right|A view of the [[Tuwaiq]] escarpment from the west.]]
[[Image:Harrat Al Birk, Saudi Arabia.jpg|thumb|[[Harrat al Birk]] volcanic field.]]
The western coastal escarpment can be considered two mountain ranges separated by a gap in the vicinity of [[Mecca]] in Tihamah. The northern range in the Hejaz seldom exceeds 2,100 meters, and the elevation gradually decreases toward the south to about 600 meters. The rugged mountain wall drops abruptly to the sea with only a few intermittent coastal plains. There are virtually no natural harbors along the Red Sea. The western slopes have been stripped of soil by the erosion of infrequent, but turbulent rainfalls that have fertilized the plains to the west. The eastern slopes are less steep and are marked by dry river beds ([[wadi]]s) that trace the courses of ancient rivers and continue to lead the rare rainfalls down to the plains. 

Scattered oases, drawing water from springs and wells in the vicinity of the wadis, permit some agriculture. Of these oases, the largest and most important is [[Medina]]. South of Hejaz, the mountains exceed 2,400 meters in several places with some peaks nearing 3,000 meters. 
The eastern slope of the mountain range in Asir is gentle, melding into a plateau region that drops gradually into the Rub al Khali. Although rainfall is infrequent in this area, several fertile wadis, of which the most important are the Wadi Bishah and the Wadi Tathlith, make oasis agriculture possible on a relatively large scale. 

Extensive lava fields (harrat) scar the surfaces of the plateaus east of the mountain ranges in the Hijaz and give evidence of fairly recent volcanic activity. The largest of these beds is Khaybar, north of Medina; another is [[Al Harrah, Saudi Arabia|Al Harrah]], part of the large volcanic field [[Harrat Ash Shamah]].<ref name="Hamawi, Mu'jam Al-Buldan p. 219">Yaqut al-Hamawi, Mu'jam Al-Buldan, vol. 2, p. 219</ref>