The Olduvai Gorge or Oldupai Gorge in Tanzania is one of the most important paleoanthropological sites in the world; it has proven invaluable in furthering understanding of early human evolution. A steep-sided ravine in the Great Rift Valley that stretches across East Africa, it is about 48 km long, and is located in the eastern Serengeti Plains within the Ngorongoro Conservation Area in the Arusha Region, about 45 kilometres from Laetoli, another important archaeological site of early human occupation. The British/Kenyan paleoanthropologist-archeologist team of Mary and Louis Leakey established and developed the excavation and research programs at Olduvai Gorge which achieved great advances of human knowledge and world-renowned status.
The gorge takes its name from the Maasai word oldupai which means "the place of the wild sisal" as the East African wild sisal grows abundantly throughout the gorge area. Twenty-five kilometers downstream of Lake Ndutu and Lake Masek, the gorge cuts into Pleistocene lake bed sediments up to a depth of 90 m. A side gorge, originating from Lemagrut Mountain, joins the main gorge 8 km from the mouth.