The Ileret area northeast of Lake Turkana in northern Kenya occupies about 700 km˛.  The area contains one of the most complete stratigraphic sequences of the Koobi Fora Formation (Pliocene and Pleistocene), and is renowned for its abundant mammalian fossils that include rare specimens of hominids.  Although the geology of the Ileret area has been studied since 1969, published stratigraphic information on the character of strata in this region is scant.  Existing good descriptions of some parts of the stratigraphy are in theses, which are not easily accessible to many workers.

Strata in the area belong to the Omo Group composed of Pliocene and Pleistocene deposits in the TurkanaBasin of southern Ethiopia and northern Kenya.  Kenyan deposits include the Nachukui Formation west of Lake Turkana, and the Koobi Fora Formation east of the lake.  The Shungura, Usno, Nkalabong, and Mursi Formations are correlative deposits in the lower Omo Valley, Ethiopia.  All eight members (Lonyumun, Moiti, Lokochot, Tulu Bor, Burgi, KBS, Okote, and Chari) are now identified in the Ileret area.

The area discussed is about twice as large as that covered previously, and covers ~200 km² not previously described.  The composite thickness (513 m) of section from the base of the Lonyumun Member to the top of the Chari Member is more than twice that reported by earlier workers, but it compares well with the thickness of the composite section of the Koobi Fora Formation.  Several new tephra correlations between the Koobi Fora Formation to the Nachukui Formation provide information on new time intervals previously unknown in the Koobi Fora region.  The new stratigraphic column for the area enhances our understanding of the geologic evolution of the Ileret area and the TurkanaBasin during the Pliocene and Pleistocene Epochs.  In addition, the new stratigraphy provides a very refined framework for fossils and artifacts collected within the area.