The southern frontier of the desert was far to the north of where it is now, while semiarid grassland and shallow freshwater lakes covered much of what are now arid plains.

过往沙漠的南部边界比现在的边界更靠北，而半干旱的草原和较浅的淡水湖泊覆盖了现在干旱平原的大部分地区。