No.18

45 km long, nearly north-south oriented, with a dendritic trough valley. The upper reaches are generally wider than 1.5 km, with depths exceeding 500 m; the lower reaches are typically wider than 2km, with depths over 1000 m. The valley entrance is a box canyon controlled by extensional fractures, and the “Xikang-type” folds are most typical and concentrated in this valley.