The mountains begin in the north, forming the Musandam peninsula. From there, the Northern Hajjar (Hajjar al Gharbi) runs southeast, parallel to the coast but moving gradually further away as it goes. The central section of the Hajjar is the Jebel Akhdar (9,834 feet (2,980 m)), the highest and wildest terrain in the country. Jebel Akhdar (and the smaller Jebel Nakhl range) are bounded on the east by the low Samail Valley (which leads northeast to Muscat). East of Samail are the Eastern Hajjar (Hajjar ash Sharqi), which run east (much closer to the coast) to the fishing town of Sur, almost at the eastern point of Oman. The mountains extend for 500 km in total.
The low coastal land north and east of the Jebel Hajjar is named Al Batinah Region (the belly), and the terrain inland of the mountains is Ad Dhahirah (the back).
The mountains are an important ecoregion, the only habitat in eastern Arabia above 2,000 m elevation. The climate is cool and wet from December to March and warmer but still with occasional rain from April to September
