The Simpson Desert is a very dry part of Australia. It is mainly in the Northern Territory, but also in the north of South Australia and western Queensland. It covers about 176,500 square km, about 2.3% of Australia. The Simpson Desert gets less than 150 ml of rain each year. It is made up of big red sand dunes up to high, long and about apart. At most times there is no surface water, but after rain there can be rivers which flow into normally dry lakes. Temperatures in summer can be more than 50 C, and in winter can be below 0 C.