A strikingly inhospitable environment surrounds this chain of oases: the snow-capped Qilian Mountains (the so-called southern mountains or Nanshan) to the south; the Beishan (northern mountains) mountainous area, the Alashan Plateau, and the vast expanse of the Gobi desert to the north. Geologically, the Hexi Corridor belongs to a Cenozoic foreland basin system on the northeast margin of the Tibetan Plateau.