Abstract: The discovery by Birger Bohlin of a series of vertebrate fossil sites in the twin lakes region(Tuosu Nor and Keluke Nor) of eastern Qaidam Basin during the Sino-Swedish Expedition in 1931 and 1932 was a major milestone in vertebrate paleontology for the Tibetan Plateau. Qaidam fossil mammals collected by Bohlin stillrepresent the best collections from the plateau and serve as an important reference point for a period of time that saw dramatic climatic changes. The more than 4600 m of strata in eastern Qaidam. spanning over 13 million years in time, are ideal for establishing a detailed biostratigraphic record, but Bohlin's published specimens lack any reference to stratigraphy, which causes much confusion about the nature of his "Tsaidam Fauna." Bohlin did, however, make a fairly detailed documentation of locality information, much of which remains buried in archival records in Stockholm. This paper is an attempt to reconstruct Bohlin's fossil localities by synthesizing relevant archives and historical accounts, as well as field observations of our own during the past 13 years. Fieldnotes in Swedish are translated to English and several field sketches are published for the first time. As a result, we are able to relocate many fossil localities that are of stratigraphic and taxonomic importance. Bohlin mainly collected in three major areas, along the northwestern shore of Tuosu Nor, south of Huaitoutala. and south of Quanshuiliang train station, each with stratigraphic settings of their own. In his published descriptions, all fossils are included in his "Tsaidam Fauna."With the help of his notes and sketches and our field verification. we are now in a position to recognize at least three faunal horizons among Bohlin's collections: middle Miocene (Tunggurian) Olongbuluk Fauna, early late Miocene(early Bahean) Tuosu Fauna, and early Pliocene(Yushean) Huaitoutala Fauna.Of these fossil sites, Bohlin’s Tuosu Nor locality is the best constrained within the modern stratigraphic framework due to the relatively short section present along the northern bank of Tuosu Nor. His fossil localities are confined to a narrow band of about 100 meters in total thickness. Bohlin’s Huaitoutala (Ulan-utsur) localities are, however, more scattered both spatially and stratigraphically. Fortunately, only a few localities produced fossils of biochronologic significance, and most are low in the section, probably belonging to the Olongbuluk Fauna. The majority of Bohlin’s Qaidam collections comes from what he informally called the “general strips,” which is not far from the present day Quanshuiliang railway station. Approximately 250 m of strata extend laterally for several kilometers. Almost all endemic bovids that Bohlin described, such as Tsaidamotherium,Olonbulukia, Qurliqnoria, Tossunnoria, are produced from this area. The Quanshuiliang region also produces some of the earliest occurrences of Hipparion in China. Preliminary correlation of the Quanshuiliang section with an existing magnetic section in Huaitoutala suggests that the local first appearance of Hipparion is close to the boundary between chrons C5r.1r and C5r.1n, about 11.1 Ma.