Two billion and twenty-three million years ago, give or take four million, something struck here and left a crater 170 to 300 kilometres across, bigger than Chicxulub, which makes this the largest verified impact structure on Earth. You cannot see a crater because there is not one left; erosion has taken 7 to 11 kilometres of rock off the top since. What survives is the deep root of it, a dome of upturned strata about 100 to 120 km wide with shatter cones and planar deformation features in the rock, which is how Dietz and Hargraves proved the impact origin in 1961. For prospectors the consequence is enormous: the strike deformed the Witwatersrand Basin and tilted its gold reefs up where they could be found, and the article on it puts it plainly, that without this impact the gold would never have been discovered. UNESCO listed 30,000 hectares in 2005. Free State, about 120 km southwest of Johannesburg.
Free State, South Africa
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