[6] They are located on the north-east corner of the Arabian Plate, reaching from the Musandam Peninsula through to the east coast of Oman.

The range is about 100 km (62 mi) wide, with Jabal Shams being the highest peak at 3,009 m (9,872 ft) in the central region of the mountains.

This episode saw the reactivation of cretaceous thrust faults and the development of long and short wavelength folding of Paleocene marine sediments that infilled previous foredeep accommodation.

Low temperature thermodchronometry of apatite grains has given ages to this deformation and subsequent exhumation of the mountain belt.

Group two are a middle Permian to Late Cretaceous sequence of continental shelf carbonates, which were deposited unconformably above the basement.

[15][16][17][18][19][20][21] The high topography is around two major culminations: Jabal Akhdar and Saih Hatat, which are large scale anticlines.

[24] The common view is that these eclogites were originally basic volcanic rocks within the leading edge of the continental crust of the Arabian Plate.

[29] This indicates that the uplift that created the present day topography occurred in the past, possibly before the initiation of the Zagros collision, by a mechanism that is not fully understood.

Generally, ophiolites are obducted prior to continental collision, which highly deforms the structure of the original oceanic crust.

The latter[40] and the smaller Jebel Nakhl range are bounded on the east by the low Samail Valley (which leads northeast to Muscat).

The mountains to the west of Sama'il Valley, particularly those in Musandam Peninsula and the UAE,[43] are known as the Western Hajar (Arabic: ٱلْحَجَر ٱلْغَرْبِي, romanized: Al-Ḥajar Al-Gharbī),[44] also known as the "Oman proper".

[1][43] In the region of Tawam,[45] which includes the adjacent settlements of Al-Buraimi and Al Ain, on the border of Oman and the UAE Emirate of Abu Dhabi, lies the outlier of Jebel Hafeet, which measures 1,100–1,400 m (3,600–4,600 ft) in height.

[56] The mountains bordering the Shamailiyyah (شَمَيْلِيَّة) coast on the Gulf of Oman, forming parts of the northern UAE Emirates of Sharjah, Ras Al-Khaimah and Fujairah,[43] may also be called the Shumayliyyah (شُمَيْلِيَّة).

The vegetation changes with altitude, the mountains are covered with shrubland at lower elevations, growing richer and then becoming woodland, including wild olive and fig trees between 3,630 and 8,250 ft (1,110 and 2,510 metres), and then higher still there are junipers.

Fruit trees such as pomegranate and apricot are grown in the cooler valleys and in places there are rocky outcrops with little vegetation.

The endangered Arabian leopard (Panthera pardus nimr) had been recorded here,[57] particularly in the area of Khasab in northern part of the Musandam.

[67][68] For example, in February 2019, an Arabian caracal was sighted here,[69][70][71] and in March, a Blanford's fox,[72][73] which has also been reported in the mountains of Ras Al-Khaimah.

[75] The Hajar are extensively grazed by domestic goats, camels and donkeys and the landscape has been cleared in parts for urban areas and for mining, which has damaged both vegetation and water supplies and uprooted traditional rural land management behaviours.

The Oman government has created the Wadi Sareen Reserve and an area of Jebel Qahwan-Jebal Sebtah in the Eastern Hajar, for the protection of Arabian tahr and mountain gazelle.