The United Arab Emirates consists mainly of sandy desert. It is bounded on the west by an immense sebkha, or salt flat, extending southward for nearly 112 km (70 mi). The eastern boundary runs northward over gravel plains and high dunes until it almost reaches the Hajar Mountains in the Ra's Musandam near Al 'Ayn. The flat coastal strip that makes up most of the United Arab Emirates has an extensive area of sebkha subject to flooding. Some sand spits and mud flats tend to enlarge, and others enclose lagoons. A sandy desert with limestone outcroppings lies behind the coastal plain in a triangle between the gravel plain and the mountains of the east and the sands of Sa'udi Arabia to the south. Far to the south, the oases of Al-Liwa' are aligned in an arc along the edge of dunes, which rise above 90 m (300 ft).
The main gravel plain extends inland and southward from the coast of Ra's al-Khaimah to Al 'Ayn and beyond. Behind Ra's al-Khaimah and separating Fujairah from the Persian Gulf is an area of mountains that rise over 900 m (3,000 ft) in height, with isolated cultivation. Finally, alluvial flats on the Gulf of Oman fill the bays between rocky spurs. South of Khor Fakkan (Sharjah), a continuous, well-watered fertile littoral strip known as the Batinah Coast runs between the mountains and the sea and continues into Oman. There are, in addition, many islands, most of which are owned by Abu Dhabi. These include Das, the site of oil operations, and Abu Musa, exploited for oil and red oxide.