The western coastal escarpment can be considered two mountain ranges separated by a gap in the vicinity of Mecca. The northern range in the Hijaz seldom exceeds 2,100 meters, and the elevation gradually decreases toward the south to about 600 meters around Mecca. 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 (wadis) 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 settled agriculture. Of these oases, the largest and most important is Medina.

South of Mecca, the mountains exceed 2,400 meters in several places with some peaks topping 3,000 meters. The rugged western face of the escarpment drops steeply to the coastal plain, the Tihamah lowlands, whose width averages only sixty-five kilometers. Along the seacoast is a salty tidal plain of limited agricultural value, backed by potentially rich alluvial plains. The relatively well-watered and fertile upper slopes and the mountains behind are extensively terraced to allow maximum land use.

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, a number of fertile wadis, of which the most important are the Wadi Bishah and the Wadi Tathlith, make oasis agriculture possible on a relatively large scale. A number of extensive lava beds (harrat) scar the surfaces of the plateaus east of the mountain ranges in the Hijaz and Asir and give evidence of fairly recent volcanic activity. The largest of these beds is Khaybar, north of Medina.

Data as of December 1992