@hyc @VeroniqueB99 Not all mountain ranges were formed the same way or at the same time. Some formed before the great divide, as is the case here. In the Permian period, the Central Pangean dealt with physical weathering that decreased the peaks and formed intermontane plains. By the Middle Triassic, the mountain sierras had lost most of their size. In the Jurassic period, the Pangean became separated by deep marine basins that later became oceans.