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 (30 mi) long, and is located in the eastern Serengeti Plains in the Arusha Region not far, about 45 kilometres (28 miles), from Laetoli , another important archaeological site of early human occupation. The British/Tanzanian 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.