Large concentrations of rock art, found in the Pilbara region of Western Australia, offer a wide variety in style, antiquity, and purpose of the petroglyphs. There is a correlation between the distribution of the petroglyphs and the occurrence of certain types of rock. Rock paintings are also discussed. The form of graphic art evolving in a region is generally that which is the most suited to the most widely available medium. The style of petroglyphs is adapted to geological conditions; rock paintings occur where suitable rock shelters are available; and where rock art cannot develop, sand designs, stone arrangements or dendroglyphs may evolve instead. Comments on this study are provided by John Clegg, David R. Moore, and Robert G. Bednarik, with author's response to these criticisms. -- AATA