Olduvai Gorge (ōlˈdəwāˌ, –vāˌ) [key], a feature of the E African Rift Valley in Tanzania. Erosional processes have exposed geological strata in the gorge dating to the lower Pleistocene epoch, about 1.8 million to 600,000 years ago. The site was made famous by the numerous hominid fossils excavated by Louis Leakey and his wife, Mary Leakey, as well as by later researchers. Examples of at least three species of hominids have been found at Olduvai, including Australopithecus boisei, Homo habilis, and Homo erectus. In addition, the two earliest stone tool traditions, Oldowan and Acheulian (see Paleolithic period), have been found along with fossil remains. Both the fossils and the tools have been important lines of evidence in understanding human evolution. Recent research in Olduvai has centered on excavated camp sites addressing problems involving the social and dietary adaptations of early hominids.