The water of the GAB is held in a sandstone layer laid down by continental erosion of higher ground during the Triassic, Jurassic, and Lower Cretaceous periods. At the time when much of what is now Australia was below sea level. The sandstone was then covered by a layer of marine sedimentary rock. This formed a confining layer, trapping water in the sandstone aquifer. The eastern edge of the basin was uplifted when the Great Dividing Range formed. The other side was created from the landforms of the Central Eastern Lowlands and the Great Western Plateau to the west. 