It covers about 140,000 square kilometres (54,000 sq mi), or a little less than 2% of the continent.
The landscape is generally flat and sandy but there are several major features, in particular the Stirling Range near Albany, which reaches 1,096 metres (3,596 ft) at its highest point, and the Darling Scarp.
Summers are warm to hot and dry, winters are cool and wet.
Mountains near the coast concentrate rainfall in that area, with parts of the extreme south-western corner receiving as much as 1,400 mm (55 in) per year.
Away from the coast, however, precipitation drops rapidly, with inland areas averaging about 250 mm (10 in) per year.