In Central and East Asia, the Upper Paleolithic dates as early as 45 ka cal BP, but until recently, there was little reliable information concerning human occupation during the following period, between 45 and 40 ka cal BP. Here we present results of the excavation of the site of Tolbor-21, in the Selenga drainage system, Northern Mongolia. We focus on Tolbor-21 Archeological Horizon 4 (AH4), an archeological assemblage that documents human occupations that fall stratigraphically and chronologically between the Initial and the Early Upper Paleolithic. We report on the spatial distribution of the finds, the zooarcheological and the lithic data to determine which of the observations reflect post-depositional processes, and which are informative of human behavior. Our initial results presented here show evidence of reworking and preservation bias on a succession of occupations, the exploitation of medium/large herbivores, and a potential structured use of space. At the regional level, our results suggest that improving the resolution of data collection may identify previously undocumented episodes of human occupation. At a broader scale, the Tolbor-21 AH4 assemblage brings new perspectives on the development of the Early Upper Paleolithic in Central and Northeast Asia.