Abstract: The study of eolian deposition in Western Loess Plateau is one of important problems in resent paleoclimate studies, but the age of the Cenozoic eolian deposition is still in dispute. The lithologic features of Xianshuihe Formation developed in Late Oligocene in Lanzhou Area are similar to those of eolian deposition in Loess Plateau, and it is significant to study sedimentary facies and depositional environmental systematically for understanding of the early eolian deposition in Western Loess Plateau. The study was carried out the rock magnetism, grain size, composition analysis and electron microscope analysis of Fenghuangshan Section which is 916m thick, north of Lanzhou. The results preliminary showed that: Most of the clay is non- horizontal bedding; The distribution curves, probability cumulative curves and composition characteristics of grain-size, susceptibility, elemental content, morphology of quartz grains of them are similar to those of typical loess, paleosol and red clay samples. So they are eolian deposit, which is the oldest eolian deposit of Cenozoic found in Lanzhou Area presently. The environmental proxies such as colour and magnetic susceptibility shows that this clay is much close to Quaternary Loess of Loess Plateau, which indicates that there was low temperature and dry geological environment in Early Tertiary. Sand and gravel layers appearing in Xianshuihe Formation are generally sorted poorly with non-horizontal or unconspicuous horizontal bedding, and the grain-size distribution and probability cumulative curves of them are similar to those of typical fluvial deposit, so they are fluvial deposits which may be related to the uplift of the Qinghai-Tibetan Plateau.