Oman, officially the Sultanate of Oman is a country in southwest Asia on the southeast coast of the Arabian Peninsula. It borders the United Arab Emirates on the northwest, Saudi Arabia on the west and Yemen on the southwest. The coast is formed by the Arabian Sea on the south and east and the Gulf of Oman on the northeast. The country also contains Madha, an exclave enclosed by the United Arab Emirates, and Musandam, an exclave also separated by Emirati territory. A vast desert plain covers most of central Oman, with mountain ranges along the north (Jebel Akhdar) and southeast coast, where the country's main cities are also located: the capital city Muscat, Matrah and Sur in the north, and Salalah in the south. Oman's climate is hot and dry in the interior and humid along the coast. During past millennia Oman was covered by ocean. Fossilized shells exist in great numbers in areas of the desert up to 80 km from the modern coastline.