On the Yilgarn Plateau, from near the boundary of the Southwest Australian Floristic Region, a series of ironstone ranges extend inland for over 750 kilometres. They rise barely more than 200 metres about the surrounding plains.
These small ancient ranges consist largely of banded iron formation, which has alternating fine layers of shales, siltstones, cherts and sediments rich in iron oxides. They are thought to have formed 2.5 to 3.7 billion years ago in sea water, as a result of fluctuating oxygen levels. They often harbour diverse and unique plant communities and endemic (found nowhere else) or unusual species. Surveys on 24 ranges have recorded more than 900 plant species, of which 44 are specialist ironstone species, as well as 134 floral communities.