Understanding how low-relief surfaces near SE Tibet edge survived from regressive erosion. Strong monsoonal precipitation on the plateau, such as during the Miocene Optimum, destroys it. Orographic effect preserves the plateau edge and reproduces the slope of the Yalong River. The narrowness of the Yalong gorge is reproduced by an upstream water inflow, carving deep valley. In the flat headwater, previously endorheic, hillslope processes dominate the landscape evolution.