The Gawler Ranges in the northern Eyre Peninsula is renowned for rocky gorges, seasonal water flows, colourful wildflowers and spectacular volcanic rock hills. Like the Ranges themselves, the area to the south has a rich geological history and is renowned for its granite rock outcrops. These rock formations are believed to have been formed around 1,585 million years ago when granites were injected into the volcanic rock. There were later eroded and exposed as bizarre outcrops, with their flared slopes, caves and gnammas. They are now among the most ancient and unspoilt attraction on Eyre Peninsula and include Mt. Wudinna (South Australia's largest exposed monolith), Polda Rock, Turtle Rock, Yarwondutta Rock, Waddikee Rock (an exposed granite dome), Pildappa Rock, Corrobinnie Hill boulders and caves and the stunning Tcharkuldu Rock.
The most southerly outcrop, known as Murphy's Haystacks, is located approximately 40km south of Streaky Bay. The term "Haystacks" is something of a misnomer. These haystacks have nothing to do with farming and are in fact very fine examples of weathered granite inselberg structures including boulders and pillars. Upon entering the viewing area a unique and magnificent Tafoni structure can be seen towering above the walkway. Elsewhere within the viewing area a variety of wave forms and flared rock structures can be seen. These are indicative of ancient physical and chemical weathering processes occurring when soil levels were several metres higher than now. These inselbergs are exemplified by finely sculpted pink granite forms that are often encrusted with lichen growths. Located near to the entrance of Murphy's Haystacks is a picnic area with toilet facilities.
Murphy's Haystacks are believed to have been weathered and sculpted into their present form about 100,000 years ago. Geologists say the Stacks are composed of pink granite from the Hiltaba suite of rocks that were laid down some 1500 million years ago. Amazingly these beautiful pink granites were formed at a depth of 7 to 10 kilometres below the earth's surface. Clearly a great deal of erosion has occurred since the granite's formation.
Local legend says that Murphy's Haystacks acquired their name from an Irish agricultural expert who saw this landmark in the distance whilst travelling on a coach. Apparently the learned Irish gentleman was very impressed and informed his fellow passengers that the farmer must have harrowed his land to produce such a great abundance of hay! The original farmer of the land was a Mr. Murphy and to this day the landmark is known as Murphy's Hay Stacks.
Arguably the best inselberg on Eyre Peninsula is Pildappa Rock which is located approximately 20 kilometres from Minnipa. Both Ucontitchie Hill and Pildappa Rock exhibit a wide range of well developed inselberg structures very different to those found at Murphy's Haystacks.