It occupies the portion of Australia west of a line running north-south roughly from the eastern shore of Arnhem Land on the Bay or Gulf of Carpentaria to the Eyre Peninsula in the state of South Australia, and skirting to the west of the Simpson Desert in the interior. The plateau has an average elevation of between . The shield is fractured into a number of distinct blocks, including two cratons - the Pilbara Craton in the North and the Yilgarn Craton in the Southwest. These two cratons are the oldest part of the shield, both of which have been dated at more than 2.3 billion years old. Some of these blocks have been raised to form uplands; others have been depressed, forming lowlands and basins. The lowlands include the Great Sandy Desert, the Gibson Desert, the Great Victoria Desert and the Nullarbor Plain, which are located in the north-western, central, southern and south-eastern shield areas respectively. The Nullarbor (from Latin, no trees) is an arid, virtually uninhabited limestone plateau. Between the Western Australian Shield and the Great Dividing Range is the Great Artesian Basin region.