Exploring the Crystals and Swirls of the Igneous and Metamorphic Rocks at Sugarloaf Rock
Sugarloaf Rock is close to the top of most people’s Margaret River bucket list. The monolith rises from the Indian Ocean close to the northern end of the Capes region, just a few kilometres from Cape Naturaliste Lighthouse. It has been the focus of many sunset photos and selfies, and rightly so, it is quite stunning.
Jed and I have visited this location a number of times in the past, either to try some photography or passing whilst hiking the Cape to Cape Track. As a geologist, I have long appreciated the beauty of the granitic boulders and the intricate patterns of light and dark minerals clustering and mixing. We recently had a little mini-break in the area and decided to dedicate a little time to really exploring the outcrop. I wanted to understand the events which created this landscape.
The approach to Sugarloaf Rock gives you multiple glimpses of the rock. The large car park is thoughtfully designed such that you can park with an unobstructed view north over the surf and coastal cliffs to Cape Naturalise Lighthouse. If you happen to arrive during a rain shower, you can enjoy a picturesque outlook from the comfort of your car.
From the car park a short paved path leads up some steps to an observation platform. This is a great starting point but a large family had assembled at the top and were taking photos so, not wanting to disturb them, we headed straight down around the base of the lookout to the rocky shoreline.
There is not a marked trail around the shore and the dirt trail only extends about a hundred metres before running into boulders. From here there is no trail and caution must be taken whilst scrambling over the rocks.
Sugarloaf rock itself is one of three granite elevations to the west of the lookout, and the only one separated by the sea. To the south is a rocky peninsula that juts out into the ocean about the same distance as Sugarloaf Rock. To the north, where we began, is a smaller granite mound that is accessible over low-lying rubble. During very high tides and storms this area may be inundated with waves and so has slippery areas and unstable boulders. It is also an area with some really interesting outcrops and is the easiest accessible with a small child.
Maddie is sixteen months now and fully competent at walking and climbing. She loves climbing! If left to her own devices I’m sure she would have great fun scuttling over and around all these boulder obstacles. But being so close to the ocean, and the unstable nature of these heavy boulders, we kept a keen eye on her. Jed held her on his shoulders for most of the time. Still, she enjoyed pointing out the birds and spotting crabs. She has mastered the words “sea”, “sky” and “star” and repeated these excitedly as Jed toured her around the formations. Maddie calls the sun “star” by the way and I don’t correct her as, technically, she is correct.
Some Geological Background
The coast of Western Australia from Geraldton to just south of Perth runs in a relatively straight, north-south line. The entire Margaret River and Capes Region juts out sharply to the west of this regional north-south coastal trend. From Bunbury the coast curves to the west, past Busselton and to Cape Naturaliste. The Cape Naturalist Lighthouse marks the northern terminus of the Cape To Cape Track that runs down the coast to Cape Leeuwin in the south.
This coastal geometry is no fluke; it is controlled by the underlying geology – a fascinating history of mountain building, continental collision and supercontinent breakup.
Most of the south-western third of Western Australia sits on what is known as the Yilgarn Craton, an almost three billion year old slab of continental crust. The Darling Ranges mark the westerly extent of the Yilgarn Craton. A large extensional fault called the Darling Fault separates the igneous and metamorphic rocks of the ancient craton with the younger sedimentary rocks of the Perth Basin.
The Perth Basin runs from Shark Bay along the coast, down through the Margaret River region to the southern coast. It slopes gently from the Darling Ranges across the Swan Coastal Plain and out to sea throughout its length – except in the Margaret River Region.
Something interesting is happening between the Cape Naturaliste and Cape Leeuwin lighthouses. We call this area the Leeuwin-Naturaliste Ridge. The granitic rocks here probably first formed about one and a half billion years ago when what is now India collided with this part of Australia in the formation of the super continent Gondwana. There would have existed a massive mountain range here, similar to the Himalaya today. The enormous pressures and temperatures involved in crashing together two massive continents means some of the granite is metamorphosed – its minerals partially melt and rearrange to form new rock types.
Somehow, in the later breakup of Gondwana, this Leeuwin-Naturaliste Ridge was torn from the main Yilgarn Craton, and sediments deposited between. In the billion or so years since its creation this mountain range has been eroded and its foundation is all that remains. This is what we were climbing around on at Sugarloaf Rock.
Babies and Metamorphic Rocks
Maddie was enjoying looking at all the pretty colours and patterns in the rock. The granites are a soft pink with some large crystals, easily visible to the naked eye. Maddie sat picking at these crystals for a little while before giving up and tottering on to the next curiosity. We had fun pointing out the swirls and shapes imprinted in the rock as grey metamorphic rock called gneiss interacts with the pink granite. The small cliffs are criss-crossed with veins of a dark grey rock called dolerite. It is funny to think that these boulders in which we play once sat beneath tens of kilometres of mountain.
As we walked around the base of the look out and back towards the car park we passed a small undercut cliff of limestone, a much younger rock. The limestone contains some fossilised burrows and calcified remains of vegetation and root systems called rhizoliths. One of these rhizoliths has eroded to form a natural bowl. I’ve heard it called the “flowerpot” and this is quite appropriate as small plants grow in the top.
We continued around and climbed back up to the viewing platform and let the toddler run around and climb on the little wall. The problem with choosing to carry her through most of our little expedition was that she hadn’t had much chance to burn off some energy – and boy does she have some energy!! We have found that if we don’t give her three or four hours of running (and I mean running, not sitting and playing) time she doesn’t want to sleep in the evenings.
Because of this we have changed how we holiday Down South, or “Douth” as Perthites call it. We used to drive between our favourite spots that were an hour or so apart, but for the first time we stayed and played just in the north of the region between Yallingup, the Cape Naturaliste Lighthouse and Dunsborough. We spent a lot more time in each location, relaxing, not much of a plan, and less time in the car.
This is one of the ways I think having children can slow you down. In a good way I mean. It’s good not to rush around all the time. Not cram too much into one day. We had planned a short hike on the Cape to Cape Track for the next day so wanted to give her time to play freely.
We spent a lazy afternoon playing at the campsite where we were staying in Yallingup. It was right on the beach and opposite the most amazing little play park. If you hang around long enough you can spot the odd pro surfer or two.
I know Maddie is too young now to understand when I tell her about the rocks and stories of past events, but I hope that in sharing these experiences with her we spark some curiosity in our natural world. I hope that she grows up to be a conscientious person, respectful of our planet and confident in her interests.
If nothing more comes of it then fun time together as a family, I’m really very happy with that.
Read More adventures from Margaret River: Family Hike along the Cape To Cape Track
More expeditions from around Western Australia:
- Family Fossil Hunting in Kalbarri National Park
- Conservation and Land Regeneration at Wooleen Station
- Southern Lights and Living Fossils at Lake Clifton