Omo is the name of the southern reaches of the Gibe river system which has its sources in the volcanic ranges south of the River Abbay (Mount Balballa, 3,261 m a.s.l.). The river opens up its course, interrupted by waterfalls, through lower cenozoic volcanic strata and flows after about 800 km into the salted water of Lake Turkana. Although several explorers had seen the delta on the northern bank of the lake, Europeans did not known that this was the Omo River until the Bottego expedition of 1896. Where the river flows out of its gorges it spreads in wide meanders into a loamy plain which is floaded during the rainy season.
The banks of the Omo canyon are densely populated by a great variety of ethnic groups speaking diverse languages belonging to different language families. The region is divided between Nilo-Saharan languages speakers to the east (e.g. Mursi, Bodi, Nangatom, Turkana), Omotic languages speaker to the west (Bashada, Aari, Benna, Karo, Hamer), and the Cushitic-speaking Dessanech, to the south. They mostly live in its lower valley, growing cereals after the floods and keeping cattle.
As the Omo gorge sunk down deeper it was filled with lacustrine and fluvial sediments where human fossiles were buried. For this reason, the Lower Omo Valley outstands prominently in the history of research on human evolution and represents one of the oldest Ethiopian palaeoanthropological research areas, exploited by a diversity of teams. Thousands of fossils have been collected in the hundreds of investigated localities. They are now preserved at the National Museum of Ethiopia in Addis Ababa and represent more than 150 animal species (various antelopes, monkeys, hippos, and pigs), most of them now extinct. These, together with fossil plants and pollens, provide a detailed picture of the Omo Valley environments in the remote past. Several hominids inhabited these environments and left remains of their activities in the various geological formations so that the fossil collection from the Lower Omo Valley is regarded as a critical reference for studying environmental, biological, and cultural evolution and is intensively used to explore the connections between climatic changes and human evolution.