The world's greatest gold-field area is located in the Witwatersrand mountain ranges of South Africa. The Witwatersrand is a a 56-kilometre-long, north-facing scarp in South Africa. It consists of a hard, erosion-resistant quartzite metamorphic rock, over which several north-flowing rivers form waterfalls. The Witwatersrand plateau forms a continental divide, with the run-off to the north draining into the Indian Ocean through the Crocodile and Limpopo rivers.