Monolith at Oldupai Gorge Archeology Dig Site in the Great Rift Valley, in the eastern Serengeti of Tanzania, site of discovery of earliest human remains. Oldupai Gorge Archeology Dig Site is where Mary Lekey found Australopithicus boisei (Zinjanthropus) skull in 1996 and evolution records from 2 million to 15 thousand years ago.