The Hajar Mountains parallel the east coast of the UAE. At their highest point in the north, in the Musandam Peninsula (Oman), they reach a height of 2000 meters. There the mountain slopes drop directly into the sea. This area is known locally as the Ru'us Al-Jibal, literally the 'heads of the mountains.'
Along the west side of the Hajar mountains are a number of westward flowing wadis or valleys penetrating far back into the higher hills. A few, such as Wadi Ghayl, hold permanent running water. Two species of fish are found here, the Arabian killifish, and a member of the carp family with no common name but endemic to the UAE and northern Oman. The latteris able to negotiate steep damp surfaces, presumably as an aid to survival, allowing it to reach upstream pools during drought. There are no frogs in the UAE, but sharing pools with these fish may be Arabian toads.