The Makgadikgadi Pan, a salt pan situated in the middle of the dry savanna of north-eastern Botswana, is one of the largest salt flats in the world. The pan is all that remains of the formerly enormous Lake Makgadikgadi, which once covered an area larger than Switzerland, but dried up several thousand years ago.
Thanks for the info. You can clearly see the remnant of the pan on Google Earth.
Obviously, we're talking about a different climate than prevails today. I wonder what the dating actually is...