The Hohsi Corridor is long, narrow and easily passable. Over 1,000 kilometres in length, it is bordered on the south by the Chilien Mountains and on the north by the broken, slightly lower Peishan Mountains. It is penetrated by the rolling sand from Inner Mongolia. The corridor, though an arid area, is constantly watered by the melting snow and ice from the Chiliens. The irrigation system here goes back 2,000 years, when agriculture was originally developed on the oases on which most of the towns and villages have since arisen.]