Olorgesailie is situated on the floor of the Eastern Rift Valley some 40 miles (about 64 km), southwest of Nairobi. Olorgesailie area is in a lake basin that existed during the latter part of the middle Pleistocene period, probably between 200,000 and 100,000 years ago. Investigations on the site started in 1942; the researchers being Dr. and Mrs. Leakey. It has important evidence that concerns the habits and activities of early prehistoric peoples of the Acheuleus or 'Hand axe' culture.

Olorgesailie has excellently preserved biological and cultural evidence about the evolution of man.

This was made possible by heavy falls of alkaline volcanic ash from the volcano activities around the site. Subsequent earth movements made the stratigraphy and fossils available for study. Around the site stand Mt. Suswa and Mt. Longonot which are volcanic in origin, the vents of which might have contributed much to the ash which accumulated in the Olorgesailie basin. There is evidence of humid climate during part of the middle Pleistocene that is given by temporary lakes and swamps that exist in the area today. The sediments left by the lake cover an area of 50sq miles (about 80 square km) in extent.

Human tools are the most prominent of all fossils in the area. The accumulation of tool represents the actual camping places of early men. There is good evidence that human species had a tropical origin. A higher primate group was confined to this part of the world. The continent of Africa had the greatest populations of evolving hominids to which Olorgesailie gives evidence not only of local importance but also of international significance. Scientifically, the site has much to do with archaeological, Palaeontological and geological meaning.