In this paper, we present the results of new archaeological and geological research carried out in SHK Extension, a new site excavatedwithin the SHK fluvial complex (Bed II, Olduvai Gorge). The paper describes the stratigraphy of the site and its correlation with our excavation in SHK Main Site, showing that overbank archaeological accumulations in both areas are synchronous and form part of the same fluvial palaeo-landscape. On the basis of the archaeostratigraphical analysis performed, mainly geared towards defining high-resolution chrono-stratigraphical frameworks within the deposit, we report the results of a technological study of the lithic collection sorted by archaeo-units, an assessment of the integrity of the main accumulation and an exhaustive lithic refitting programme. The archaeological sequence at SHK Extension, consisting of three archaeo-units, preserves a high-density patch of lithics and fossil bones (Level B2), on an overbank setting, isochronous with the SHK Main site. The high percentage of small lithic remains and bones, large number of fresh archaeological materials, and the identification of several refit sets support the integrity of the anthropogenic accumulation documented in Level B2. The main technological trait of the lithic assemblage from this level is the preservation of a qualitatively significant sample of large flakes and LCTs. The technological behaviours observed in SHKE, in the frameworkof the SHK complex, confirm that the complex web of inter-assemblage variability during Bed II times operated also in very close fractions of the same palaeo-landscape. This reinforces the idea that subtle functional parameters must be taken into account in our current assessment of the Developed Oldowan/Acheulean interface.Fernando Diez-Mart ın (fernando.diez.martin@uva.es),