AbstractIn the middle and lower reaches of the Salawusu River, the Salawusu Formation regarded traditionally as fluvio‐lacustrine deposits actually includes a series of strata which mainly consist of eolian sandy deposits named as “Chengchuan Formation” by the authors. The eolian sand of the Chengchuan Formation and the Malan loess distributed in the upper reaches of the Salawusu River are deposits of sand and loess facies formed by wind action during the same period. The relationship of the Chengchuan Formation and the Malan Loess with the Salawusu Formation which is really of fluvio‐lacustrine deposits is that the former two superpose the latter. This can be demonstrated by the difference of the extinct species proportion of the faunas in different strata. In this area, the Salawusu formed during the early period of Late Pleistocene, while the Malan Loess and the Chengchuan Formation deposited during the late period of the Late Plei