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Dongodien (GaJi4) is a sequence of sub-lacustrine, beach, and sub-aerial lake margin sediments of the Galana Boi Formation at Koobi Fora, Lake Turkana, Kenya. The sediments accumulated under a climate of increasing aridity in the latter African Humid Period. The section contains two archaeologically rich beds (Horizons B and A). Here, we present new optically stimulated luminescence (OSL) dates that are independently corroborated with C-14. The lower bed (Horizon B) has an OSL age of 4.14 ± 0.27 ka, supported by C-14 ages of 4.71 ± 0.13, 4.79 ± 0.08, and 4.70 ± 0.06 ka cal BP. The upper bed (Horizon A) has an OSL age of 2.34 ± 0.20 ka, consistent with that of site stratigraphy. In contrast to luminescence dating attempts elsewhere in the East African Rift System, quartz-OSL from this locality and sites FwJj5 and FwJj25 ~40 km NW has a dominant fast component and robust intrinsic characteristics. OSL confirms Dongodien recorded the first known appearance of pastoralism in East Africa; it lays within a tsetse-free corridor between northern and southern Africa. Interpretation of archaeologically rich horizons as beach deposits is consistent with published lake level curves and Holocene highstands. Archaeological material (obsidian microliths, Nderit pottery, wild and domestic mammal bones, fish bones) suggests mixtures of subsistence strategies (hunting-gathering, fishing, herding) as the climate became more arid. The site may have been chosen for reoccupation because of abundant fish associated with lacustrine upwelling near Koobi Fora, a cuspate foreland.