extensive lowland in southwestern Kazakhstan and northwestern Uzbekistan and Turkmenistan. It is bounded by the Saryarqa (Kazakh uplands) in the north, the outliers of the Tien Shan, Pamir, and Alay mountains in the east, the Kopet-Dag Range in the south, and the Caspian Sea in the west. It is traversed by the lower courses of the Syr Darya and Amu Darya, both of which drain into the Aral Sea. The arid plain encompasses two deserts, separated by the valley of the Amu Darya: the Karakum (Karakum Desert) and the Kyzylkum. The deserts comprise fine-grained sedimentary rocks overlain by extensive sand dunes and sand sheets. Vegetation is sparse, comprising xerophytic (drought-resistant) scrubs and short grasses. There are a number of hills up to 3,300 feet (1,000 metres) in elevation, as well as several depressions below sea level.