The Western Desert covers about 700,000 square kilometers. The desert's Gilf Kebir Plateau has an altitude of about 1,000 meters, The Great Sand Sea lies within the desert's plain and extends from the Siwa Oasis to Gilf Kebir. Escarpments (ridges) and deep depressions (basins) exist in several parts of the Western Desert, and no rivers or streams drain into or out of the area.