The Simpson Desert is famous for its long parallel what?

The Simpson Desert is famous for its long parallel sand dunes.

The Simpson is a vast erg—an area dominated by wind-shaped sand—spread across the Northern Territory, South Australia, and Queensland. Its dunes generally run north–south and remain remarkably parallel over great distances, creating the distinctive ridged landscape associated with the desert.

Some dune ridges continue unbroken for up to 200 kilometres. Their height varies across the desert: western dunes may be only about 3 metres high, while eastern dunes approach 30 metres. Nappanerica, popularly called Big Red, rises to roughly 40 metres and is the desert’s best-known dune.

The dunes are not simply loose, constantly migrating piles of sand. Vegetation, especially spinifex and Zygochloa paradoxa grass, helps anchor many of them in place. Their asymmetrical slopes also reflect prevailing winds: the western sides are generally gentler, while the eastern lee slopes are steeper. The desert’s long dune lines are therefore both a geological signature and a major challenge for vehicle crossings.