High Quality Content by WIKIPEDIA articles! The Olduvai Gorge is a steep-sided ravine in the Great Rift Valley that stretches through eastern Africa. It is in the eastern Serengeti Plains in northern Tanzania and is about 48 km (30 mi) long. It is located 45 km from the Laetoli archaeological site. The gorge is an important prehistoric site, sometimes called "the Cradle of Mankind."