Guanzhong (lit. Center of Passes), or Guanzhong Plain, historically refers to an area that was closed by: Xiao Pass (蕭關) to the north, Hangu Pass (函谷關) to the east, Wu Pass to the south, and Dasan Pass (大散關) to the west, including central part of Shaanxi and the extreme west of modern Henan. The average altitude of the Guanzhong Plain is around 500 metres.… (More on Guanzhong)