page_title: Olduvai Gorge
section_title: Gorge Stratigraphy
hierarchical_section_title: Olduvai Gorge / Archaeology and geology / Gorge Stratigraphy
caption_attribution_description: English: View on monolith at Olduvai Gorge, Tanzania
context_page_description: 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 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.
context_section_description: The stratigraphic sequence in the gorge is up to 90 m thick, with a welded tuff, the Naabi ignimbrite, forming the base.  This is overlain by a series of lava flows from Otmoi and from another source to the south.  The oldest fossils are found on this surface, dated at 1.89 mya, while stone tools have been dated at 1.7 mya through the first use of K-Ar dating by Garniss Curtis. In addition, fission track dating and paleomagnetism were used to date the deposits, while amino acid dating and Carbon-14 dating were used to date the bones.  Hominid fossils and stone tools are found continuously throughout the entire exposed sequence in the gorge.  Faulting between 100 and 30 kya, formed the Olbalbal Depression northwest of Ngorongoro.
caption: Close-up of monolith made of red sediments from Bed III
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