The Kingdom of Saudi Arabia is about 1,969,000 km2 occupying four-fifths of the Arabian Peninsula.The eastern region lies on the Arabian Gulf coast and contains salt flats (sabkhahs).From this fertile crest it falls towards the east as a desert plateau to the dry interior or the Najd containing the Dahna and Nafud which extends to the great sand desert of the Rub Al Khali (The Empty Quarter).From the Dahna dunes to the east coast the terrain alternate between rocky outcrops and gravel plains.Western Saudi Arabia is dominated by a mountain chain running the entire length of the country, known as the Hejaz and Asir mountains.There are many artesian wells along the coast which are used to irrigate large areas under cultivation around Hofuf and Qatif.