As we left Streaky Bay (SA), travelling to Elliston, we stopped off at a pretty interesting natural phenomenon called “Murphy’s Haystacks”. They are ancient wind-worn pink granite boulders that formed 1500 million years ago. They stand like a crooked set of giant’s molars on a hilltop just 2km off the Flinders Highway. (maplink)
Folklore has them named after a Scottish agricultural expert who spotted the crop of remarkable rocks from the local mail coach. The Scotsman obviously had a fertile imagination. “That man must harrow,” he commented to his fellow travellers. “Look at all the hay he has saved.”
The owner of the land was Denis Murphy, and faster than you could shout “mine’s a Guinness!” the Murphy’s Haystacks nickname had stuck. Of course they’ve nothing to do with haymaking and are in fact great examples of weathered granite inselberg formations (German for “island-mountain”). They’re part of a larger mass called the Hiltaba Granite, named for the Hiltaba Station in the southwest Gawler Ranges, under which much of the mass lies. Ayers Rock is an inselberg.
The granite was originally hidden deep in the Earth’s crust, probably some 7-10 km below the surface, but over eons the overlying rocks have worn to be transported and deposited on the surrounding continental shelf and inland basins.