​Greetings fellow Foxies,
I recently went for a holiday to a suburb of Narrogin called Augusta. Although a trifle too wet for me, it is a pleasant town and a great spot for the amateur geologist.
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I explored Groper Bay. This is a delightful spot for a ramble, and the rocks are wonderful!
One must walk from the car park and scramble down rough tracks and rocks (see my journey on image). Note there are no trails, and the rocks are smooth. It is a good workout for a healthy 74-year-old, but not for the dodgy hip brigade
The bedrock once granite and dolerite like Narrogin has been altered and stretched. A north-south trend in rocks is evident on the aerial photo with lines of rock projecting into the ocean. 

The rocks resemble pieces of rock art due to weathering and smoothing by sand and water.
The lumpy stretched rock patterns below are called boudinage.Boudin is apparently French for their black pudding, which is made into sausages!
These rocks have been subjected to a lot of heat and pressure!
In the image below the large grained whiter and fine-grained darker rocks have remained more solid while the more plastic pinkish rock flowed past, but they were stretched and deformed into cylinder cross section rocks called boudins.

​The very picturesque cove (site 3) contains rounded boulders that vary in colour and texture from dark near the waterline, to salt bleached, then bright yellow lichen speckled adjoining the bush. It is a lovely spot but a bit lumpy for sunbathing. In spots what looks like fossilised white scum is draped over rock adjoining the soil line. This is Tamala limestone that outcrops at our beaches. Most limestone has formed in deep ocean from carbonate shell deposits, but this is different. Tamala limestone originated as coastal shell sand dunes. Mild acid from carbon dioxide and water in rainfall dissolved the shell lime and carried it to the base of the dunes where it formed a solid carbonate layer. This has been exposed by wind or wave action that removed the overlying sand. Tamala limestone is a miserable deposit compared to huge depths of limestone elsewhere. It is used for agricultural lime and building blocks and contains the caves. 

​Dark rock forming the western point was a dolerite or gabbro intrusion that has been stretched and deformed into a rock called amphibolite. At the marina fresh amphibolite is exposed at a huge rock face where the side of the hill was blown away to produce rocks for the breakwater.

​The rocks spurred me on to research their origin. Here is a simplified version of my findings.

While Narrogin is on the ancient Yilgarn craton, the capes are on a much younger rock called the Leeuwin-Naturaliste Ridge on the Pinjarra Orogen, which is west of the Darling Fault. (see this blog).
The Leeuwin-Naturaliste rocks formed as granites and mafic rock plutons intruded into a rift that formed on the Pinjarra orogen about eleven hundred million years ago. At this time Western Australia was separating from an unknown continent to the west as the Pangaea supercontinent broke apart.
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 About seven hundred and fifty million years ago while continents amalgamated again to form the Gondwana supercontinent, India obliquely collided with WA in what is a southwest direction today (Leeuwin orogeny). The collision buried the rocks where they partially melted, and the minerals were altered and stretched into roughly north-south bands (that are sometimes folded) as India also moved south. A substantial mountain range formed at the join and gradually eroded away.

About four hundred million years ago, starting from the north, India gradually began separating from WA. This caused a rift valley to form between the Dunsborough and Darling scarps that gradually filled with sediments from both sides. Today, this is the belt of sandy scrubby woodland between Bridgetown/Nannup and the Leeuwin-Naturaliste Ridge jarrah/karri forests. (Donnybrook Sunkland).
Finally, about eighty-three million years ago, Antarctica finally separated from Australia, taking the southern part of the Leeuwin-Naturaliste ridge, which is now under the Denman Glacier.

When you sip wine at the capes, pause and remember the tumultuous origin of the land you are standing on. Did the ground move or have you had enough to drink?

​Click here for a Google Photos tour of Groper Bay.

​Greetings fellow Foxies
Whinbin Nature Reserve adjoins Whinbin Rock about 20km east of Highbury on the (sealed) Whinbin Road. Although only 38 hectares in size its strategic location on a ridge provides a valuable bird breeding refuge within substantially cleared farmland. About a quarter of the reserve had been mined for gravel and sand, but this area has been replanted, and trees and other vegetation elsewhere is in good condition.

There are a range of land types, with the most common being sandy and loamy gravels, tall woodland loams and sandy duplex. There are no waterways or sheoak jam country that signifies good orchid country. On my two visits I found greenhoods, cowslips and a few fringed mantis orchids.
There are no internal or boundary roads or tracks apart from one on the south-western side that leads from Whinbin Road to a renovated sand pit.
​The northern side of the reserve has little interest for bushwalkers apart from a line of salmon gums with a few delightful understorey plants. I was surprised to see a grevillea on that loamy soil, but the plant, Grevillea huegelii is found further east.

​A walk through the southern side of the reserve takes one through kwongan bush with scattered mallees, on open wandoo on the western side, and a breakaway on the eastern side. Below the breakaway, the country varies from dense blue and brown mallet, open woodland and tammar gravel to the north east. 

​I suggest a visit to this reserve from mid-August to mid- September when many of the bushes are flowering and before kangaroo ticks become active. There is a good WIFI signal for Telstra users you can track your location using Google Maps

​Greetings fellow Foxies,
 I love climbing and understanding rocks (my wife thinks that there is mountain goat in my ancestry).
In the process of producing a Boyagin Rock brochure I climbed over and around it and compared it with our other great rock tourist destination, Yilliminning Rock. Both are inselbergs that outcrop from underlying granite basement rock that welled up when two older slabs of continental rock crashed into each other about two thousand seven hundred million (2,700,000,000) years ago. At the time volcanos erupted and a huge alpine mountain range similar to today’s Himalayas was formed. Over great time this bit of rock joined with others to form Australia and the supercontinent Gondwana, that joined more to form the global supercontinent Pangea, that then split up (greatly simplified). Very slowly the mountain range weathered and washed away.
Another mind-blowing statistic is that Yilliminning and Boyagin rocks were once part of magma chambers 5 to 7 kilometres below the ground surface. These have been exposed over eons as the overlying material was removed.
 
In the agricultural area, features like ridges, cracks and waterways tend to follow straight lines that may suddenly change from one direction to another. Our soils and the depth to crystalline bedrock are shallower than many other parts of the world. Surface features often reflect faults, intrusions and other changes in the mainly granite basement. Lines frequently trend northwest- south east, northeast -southwest, east-west, and north-south.
 
There are distinct differences between the two rocks.
Yilliminning Rock is more typical as a large granite dome arising from a gently undulating landscape.

​The Boyagin landscape is much hillier, and the rock itself is more variable. It is one of two adjoining large rocks project from the eastern side of a lateritic upland plain.
In the early morning, variations in the texture of Boyagin Rock granite can be seen in strange shapes where there has been uneven weathering of the rock. Look closely and you can see lines and mini ‘craters’ and lumpy spots on the otherwise smooth granite. 

​A look on a map shows that uplands and rivers in the Brookton area commonly trend north-south up to beyond the Avon Valley.

​An explanation goes back about 95 million years when India was once attached to, but slowly separating from WA. Brookton and surrounds were part of a plain with west-flowing rivers carrying sediment
into a rift valley that is now the Swan Coastal Plain (Perth – Bunbury etc.)
 
83 million years ago India finally separated from western WA and drifted north to crash into Asia.
With the weight of the Indian block removed, a line east of the Darling Fault from about Carnamah to the south coast bulged upwards to create the Darling Range. The land rose about 250 metres and was accompanied by other parallel downward and upward folds in the ground to its east.
 
These changes in slope completely blocked the old east-west flowing rivers and the blocked water ran down a new valley south from Dalwallinu (Mortlock North branch), and North from Pingelly (Avon South branch) into the Swan River.
The newly created Boyagin Creek then exposed Boyagin Rock.
​General north- south river systems and lines of ridges in the Darling Range can be seen on the before and after diagrams

​When I investigated the southwest base of Boyagin Rock I was surprised to see what looks like a quite recent north west-south east fault in the granite that had been exposed in a creek. 

As it turns out, generally east of Brookton is a localised earth movement hotspot in the southwest seismic zone (remember the Meckering earthquake?).
The Darling Range may also still be slowly rising so the old rocks may still be rocking. Of course the Wagyl also had a part to play.
 Click this link for a visual exploration of the rock.
Next time you climb Boyagin Rock take a good look around and be grateful for this true rock of ages.

​Greetings fellow Foxies,
 
This reserve near Tarwonga is not named on any map. The reserve is named after Michael Quinn, one of the pioneering pastoralists in the district, and whose name is preserved in the adjoining Quinn’s Pool.
It is a great area for wildflowers, bushwalking and birds because of so many pristine and varied land and vegetation types, including lovely riverside flats that have mostly been cleared for agriculture. It also contains part of an old bullock wagon trail from Wagin to Williams via camping spots at pools on the way.
About half was surveyed and fenced for agriculture but luckily not cleared. A small block was subsequently designated as a mallet reserve.
Now for the bad news. Most of the entry tracks and some internal ones cross waterways that are too deep and boggy for all but experienced four-wheel drive owners. I found a way in from Tarwonga Road, but one needs to drive on to a fairly steep road cutting to enter. OK if you have confidence and a car like my 2WD-ute that can handle the odd scratch from track-side vegetation. I also take an extra jack and recovery tracks in case I get bogged. Mobile phone reception is poor on the flats. It is a long walk to neighbouring farms, and 27kms to Narrogin.
There is a lot more to see that can be managed in one trip. I really enjoyed the frequent changes in landscape, views and vegetation while wandering through the bush. Numbers below indicate my favourite spots so far. Definitely returning next spring.

​Area 1 can be accessed by a short walk through sheoak woodland to clear “islands” of shallow granite.
This is a delightful area in August/September. I found blue fairy orchids, lemon scented sun orchids growing amongst wetland plants and everlastings.

Area 2 comprises the granite outcrops and mallet ridges further up on the crest of the hill. Walking up to it from area 1 can be a challenge due to dense regrowth of Acacia celastrifolia (great flowers in August). If you are tempted to drive directly up from the eastern boundary, there is a creek crossing that I won’t attempt in my ute in winter. Either walk up the firebreak or take a circuitous route from the (hidden) entrance on a road cutting bank further down.The walk in from the firebreak is a bit challenging via mallet ridges and dense growth, but it is worth it. I also found feral pig diggings on red soil here below a line of granite that marked an ancient fault line

​Area 3 is a long sandy gravel slope that adjoins area 2, with low breakaways on its southern and eastern edges. This is species-rich kwongan scrub with diverse new growth from a recent fire. Nice view from here, and interesting plants.

​ Area 4 is a waterway with shallow rocky soil nestled below mallet breakaways. The track up to it is eroded and a bit rough. Vegetation here is very attractive Calothamnus quadrifidus scrub dotted with Grevillea pinnatifida and Isopogon dubious shrubs. It is a lovely spot to wander around and explore

​Area 5 comprises gentle slopes and flats surrounding the two major waterways. This varies from orchid-rich shrubby sheoak and wandoo woodland, open wandoo woodland on sandy duplex soils to sand over gravel over clay open kwongan with patches of mallee. Pleasant country to have a picnic and walk around looking for orchids

For more photos of this reserve click this Google photos link