A rock of Gibraltar Range National Park - Part 1.

A lookout on the Gwydir Highway

I was going to write a very long post on the Dandahra Creek Leucogranite but I think it lends itself to two posts. This post will focus on the amazing Gibraltar Range National Park and the second will focus on Australian ingenuity and dating of the Dandahra Creek Leucogranite.

A few months ago I travelled from Glen Innes to Grafton via the Gwydir Highway. The landscape in this area is wonderfully diverse and surprisingly contradictory. For example usually Sandy soils on the plateau give rise to swamps with peat. It is a special area because the link between the geology, vegetation and even bush fire patterns is quite obvious. I'd like to focus on one rock unit that makes up the balance of the Gibraltar Range National Park area, the Dandahra Creek Leucogranite.

The Dandahra Creek Leucogranite was often referred to as the Danhahra Granite (and still regularly called this in botanical circles). It is part of the New England Batholith and has recently been dated at at 237.6 Ma (Chisholm et al 2014). It is the youngest member of the Stanthorpe supersuite of granites. Outcrops are very frequent in the Mulligans Hut area and the Gwydir highway transverses the unit.

The spectacular tors which are major features of the landscape of Gibraltar Range National Park arise from weathering from the Dandahra Creek Leucogranite. These tors form through onion peel weathering (technically called exfoliation or spheroidal weathering). This weathering process is where water enters cracks in the rocks and then freezes over night. As water turns to ice it expands and sheets off rock just like an onion skin. This is usually a fairly slow process except with the last sloughing off of the onion peel occurring quite rapidly.

Tall open forest is a major feature of the landscape of the Dandahra Creek Leucogranite. These eucalyptus dominated forests can have an open, grassy understorey featuring grass-trees and/or tree-ferns. These landscapes are quite fire prone. Indeed their structure is dependent on multi-decadal scale fires.

There are also some more unusual vegetation communities on rock outcrops because the tor outcrops lend themselves to protecting some vegetation from fires. They are also very thin soils with low nutrient content so even carnivorous plants can be found.

Heathlands and grasslands occur around the rock outcrops and are particularly important as they contain the greatest concentration of rare, threatened or geographically restricted species, or species found at the limits of their distribution (NPWS 2005). The grass and heath land burns very frequently often with bush fires only every several years.

The shallow wide valleys that are formed on the sandy granitic derived soils result in common large peat swamps. The shape of the valleys slows down water and the underlying massive granite means that the water does not infiltrate. The swamps contain sedges and other water loving plants.

If you are interested in the bush or interested in rock the Gibraltar Range National Park is for you. If you are in to camping, bush walking, amazing views of rugged valleys the Gibraltar Range National Park is for you. If you are in to spectacular flowers, rainforests, exploring a rocky creek the Gibraltar Range National Park is for you. If you are in to staying in a lodge, want to see some snow, or bathe in a rock pool on a summers day the Gibraltar Range National Park is for you.

References/Bibliography:

*Chisholm, E.I., Blevin, P.L. and Simpson, C.J. 2014. New SHRIMP U–Pb zircon ages from the New England Orogen, New South Wales: July 2012–June 2014. Record 2014/52. Geoscience Australia

*Clarke, Peter J. & Myerscough, Peter J. 2006. Introduction to the Biology and Ecology of Gibraltar Range National Park and Adjacent areas: Patterns, Processes and Prospects. Proceedings of the Linnean Society of New South Wales

*New South Wales National Parks and Wildlife Service 2005. Gibraltar Range Group of National Parks (Incorporating Barool, Capoompeta, Gibraltar Range, Nymboida and Washpool National Parks and Nymboida and Washpool State Conservation Areas) Plan of Management. February 2005. ISBN 0 7313 6861 4

Armidale submerged

Armidale is well known for its height above sea level, with some areas above 1000m it is at a relatively high altitude by Australian standards. The city is located in the New England, ‘Northern Tablelands’ which provides an indication of the landscape in which it is situated. The area resembles a very large plateau with comparatively light rolling hills compared with the nearby escarpment and edges of the tablelands. In fact, Armidale is just a tiny bit to the east of the crest of the Great Dividing Range. Surprisingly, this area was in part inundated by a lake, or lakes.

Examples of some rocks that make up the Armidale beds
The big sample at the front has been partially turned into silcrete.

One of the headwaters of the Macleay River, Dumaresq Creek flows through Armidale. In places this creek, as well as other creeks in the area, have cut through the basalt rock that covered the area. A description of this process was covered in an earlier post. In this post I’d like to describe the sediments that lie under the basalt. These are Eocene (or earlier) sediments named by Voisey (1942) the Armidale Series, now known as the Armidale beds.

The Armidale beds are comprised of fluvial (river) and lacustrine (lake) deposited sediments. These are principally conglomerates, siltstones, sandstones and shale. Interestingly, the shales are laminated possibly as a result of seasonal deposition in a lake. They also contain abundant plant fossils. The material that makes up the sediments is particularly obvious in the conglomerate. The conglomerate clasts are derived from the older underlying geology, for example clasts of jasper, quartzite and granites.

The Armidale beds occur in small remnant areas (the balance of the beds having been eroded away). These remnants occur throughout the Armidale area but almost as far away as Wollomombi to the west, near Dangars Falls to the south-east and Kellys Plains to the south-west. Voisey 1942 named this area Armidale Lake which is a palaeo-lake that only exists now in the sediments that it left. The formation of Armidale Lake occurred either before or during the volcanism that ended up covering a majority of the Armidale region in blankets of basalt lava (lavas of the Central Volcanic Province). In fact, the Armidale beds were preserved by this blanket of basalt both directly and through metamorphism beds in the area of contact. This metamorphism of the Armidale beds created a layer of hard silcrete (once known as greybilly) which itself was resistant to erosion and helped preserve the underlying un-silcretized sediment from being washed away.

The picture above is an example of the Armidale Beds that occur near the Armidale garbage disposal centre. A very accessible example is located on Madgwick Drive on the way to the University. It is actually one of the best remaining exposures of the unit and has been used for years by local schools and the university. Indeed, Banaghan & Packham 2000 have the road cutting as a stop on their Armidale-Yarowych geological tour.

References/bibliography:

*Branagan,, D.F. & Packham, G.H. 2000. Field Geology of New South Wales. Department of Mineral Resources.

*Fitzpatrick, K.R. 1979 The Armidale area. Geological Survey of New South Wales. Geological Excursion Handbook 1

*Voisey, A.H. 1938. The Geology of the Armidale District. Proceedings of the Linnean Society of New South Wales.

*Voisey, A.H. 1942. The Geology of the County of Sandon, NSW. Proceedings of the Linnean Society of New South Wales. V67.

The Road to The Gorge

Note that since this post was written the Towgon Grange Granodiorite has been renamed the Towgon Grange Tonalite.

Many people in the region know about “The Gorge”. It is a remote, yet popular area on the Clarence River. The road to The Gorge is interesting because of the change in geology that is experienced. The main route to The Gorge is via Grafton and Copmanhurst. By travelling west from Copmanhurst along the Clarence Way you move from the sedimentary rocks of the Clarence-Moreton Basin. First,  the rugged cliffs made from the Kangaroo Creek Sandstone give way to the rolling hills of the Walloon Coal Measures then Koukandowie Formation. Some road cuttings show weathered examples of these rocks. Turning off the Clarence Way and passing over the camping ground, swimming hole and bridge at Lilydale leads you to The Gorge turn-off. The Lilydale and Newbold areas have some of the oldest rocks of the Clarence-Moreton particularly the Laytons Range Conglomerate. But on the day I was there, I was not so interested in those rocks… because I was getting into the New England Orogen.

It is rare opportunity for me to explore the foot hills of the New England region. I love the feeling of the place, the wonderful landscape, climate, history and even culture. The place just seems to have a feeling of connection with the people who live there. Luckily, I managed to visit the edges of the New England escarpment for a little while on the weekend. While there I managed to experience more of the rocks that are the foundations of the landscape of New England.

Towgon Grange Tonalite - on The Grange Road, Middle Clarence River area

Driving along The Gorge road the rocks of the Silverwood Group are passed by. These are slightly enigmatic rocks of the New England Orogen, interpreted as subduction complex rocks (Van Noord 1999). Mainly outcropping in streams the rock of the Silverwood Group in this area are none the less quite hard and old metamorphosed marine sedimentary and volcanic rocks. The Silverwood Group is interesting because it also occurs near Texas in Southern Queensland and it is only partially understood in our region. But more about the Silverwood Group in a future post. 

Round tors appear by the road side near Table Creek about 15km south of The Gorge. These tors are a classical shape formed by the weathering and erosion of granite type rocks. Here are rocks that make up part of the New England Batholith. The batholith is numerous masses of intrusive igneous rocks plutons that were molten well before Australia was separate from Gondwana. The ‘granite’ here is called the Towgon Grange Granodiorite. Like the Dumbudgery Creek Granodiorite that occurs about 20-30km further north the pluton is bisected by the path of the Clarence River. This helps to illustrate the unusual behaviour of the Clarence river as it travels backward and forward over soft and hard rocks. In fact the other side of the pluton can be easily found on the other side of the river just off the Clarence Way.

The Towgon Grange Granodiorite intrudes into the Silverwood Group meta-sediments. The rock sample at Table Creek (pictured) is actually not a granodiorite. It is notionally similar in appearance but contains much less potassium-feldspar. The main minerals are light coloured plagioclase feldspar, quartz and darker clinopyroxene and amphibole. The rock sample shows that much of the clinopyroxene is mantled (surrounded) by amphibole. The lack of potassium-feldspar means that this particular sample is probably a Tonalite according to the most popular rock classification (QAPF). In fact Bryant et al (1997) actually notes that the Towgon Grange Granodiorite only contains small amounts of Granodiorite, with most being Tonalite or Quartz Diorite. This is a good example how stratigraphic names may be misleading to first time geologists!

Bryant et al (1997) classifies the Towgon Grange Granodiorite as an I-type granite of the Clarence River Supersuite. This means that the Towgon Grange Granodiorite is derived from the melting of other igneous rocks. The Towgon Grange Granodiorite is also comparatively low on silica (quartz) in comparison to other Clarence-River suite intrusions. It still contains enough quartz that it is generally visible in hand specimens. The age of the Towgon Grange Granodiorite is about 248-249Ma old. The younger sedimentary rocks of the Clarence-Moreton Basin overlie parts of the Towgon Grange Granodiorite and Silverwood Group.

The Towgon Grange Granodiorite is one of those rocks that just about no one in the general public has heard of. But, it is a good example of rocks that illustrate many points about the landscape evolution of the New England Orogen and the Clarence River. It occurs in a scenic area and is also a very attractive rock in its own right.

References/bibliography: 
*Bryan, C.J., Arculus, R.J. & Chappell, B.W. 1997. Clarence River Supersuite: 250Ma Cordilleran Tonalitic I-Type Intrusions in Eastern Australia. Journal of Petrology V.38 No. 8.

*van Noord, K.A.A. 1999. Basin development, geological evolution and tectonic setting of the Silverwood Group IN Flood, P. G. (ed.) Regional Geology Tectonics and Metallogenesis: New England Orogen - NEO '99 Conference University of New England.

It's a Demon of a Fault

Many people have requested that I do a post on the Demon Fault. I've struggled to put something together because structural geology is not one of my strong points and secondly because there was so little published information about it, except for some specific papers in the 1970’s. Thankfully, a few months ago Babaahmdi & Rosenbaum (2013) published a detailed paper summarising what was known in the 1970s, presenting how the fault appears, how it seems to have developed and how it may fit into the development of eastern Australia. It is worth noting that Gideon Rosenbaum from The University of Queensland has been the major researcher on New England structural geology for the last 5 years. If it was not for him and his student’s research we would be struggling to understand some of the basic features of the older rocks of the region including the Demon Fault.

Large faults are usually have quite distinctive landscape features. The Demon Fault is mainly a transverse type fault (movement on the fault horizontally rather than vertically) which displays very obvious topographical features.  Transverse faults often form valleys, where the rock of the fault has been broken down into what is called gouge or rock-flour. Gouge is very weak material. It is easily eroded and rivers often preferentially follow the route of the fault carving out the gouge into deep valleys.  The presence of deformational features in the surrounding rock can give an indication of how deep the fault was when it was active.

The Demon Fault is a prominent feature because it is evident from a series of valleys from near the Queensland Border to Dorrigo. At the Queensland end it is partly obscured by the Cenozoic Main Range Volcanics and in the Dorrigo area the end is obscured by the Cenozoic aged Ebor Volcanics. Geological maps of the area show a nice linear feature with obvious truncation of pre-existing geological units. Aerial photos also show the fault up nicely with streams preferentially flowing along the trace of the fault and contrasting with the rugged forested mountains surrounding it. I’ve never taken a photo of any part of the Demon Fault but a nice photo taken from an aeroplane can be found here: http://www.panoramio.com/photo/35890361

The Timbarra River has followed the Demon Fault creating linear valley
http://www.panoramio.com/photo/35890361 (used with permission)

Korsch et al (1978) observed that the Demon Fault had displaced several geological units including intrusions of the Bungulla Monzogranite (now known as the Rocky River Monzogranite), Dumbudgery Granodiorite and Newton Boyd Granodiorite as well as the Drake Volcanics. The fault was interpreted as a dextral strike-slip fault (a fault where the eastern side had moved south relative to the western side). Korsch et al (1978) calculated that the fault had displaced these units 17km which is substantial in Eastern Australia. Dating of the displaced granite intrusions provides a possible maximum date of within Triassic period (249-232 million years). The nature of deformation features adjacent to the faulting indicates that the fault was shallow and/or was created in a brittle environment. Badaahmadi & Rosenbaum (2013) speculate that the timing of the faulting may actually be similar to that of faulting and extension in the earth’s crust that formed the Ipswich and Clarence-Moreton Basins (more about this in future posts).

There are many factors in understanding the Demon Fault. It is interesting to note that other authors have come up with different lengths of displacement including 30km in the northern part of the fault and 23Km in the central part. Badaahmadi & Rosenbaum (2013) have calculated that the northern part of the fault displaced 35km, in the centre by 25km and south by 19km. Some components of reverse faulting (where one side of the fault slid down and away from the other side) were observed. Additionally, it was noted that the Demon Fault did not appear to follow one big long line but instead had numerous splays (deviations, splitting, etc) especially in the south. Badaahmadi & Rosenbaum (2013) suspect that there may be two causes to the different lengths:

1. Splays may have created movement of the fault which had a vertical component as well as horizontal.
2. There may have been some fault reactivation of the northern part of the fault as recently as the Cenozoic era.

Both of these possibilities really need a discussion in their own right, rather than cursory mention. So, I’ll get back to these in a future post.  I also want to cover the significance of the Demon Fault in formation of the Texas and Coffs Harbour Oroclines which are incredibly large features that I’ve briefly touched on in an earlier post about the South Solitary Island.

References/bibliography:
*Babaahmadi, A. & Rosenbaum, G. 2013. Kinematics of the Demon Fault: Implications for Mesozoic strike-slip faulting in eastern Australia. Australian Journal of Earth Sciences. V.60
*Korsch, R.J., Archer, R. & McConachy, G.W. 1978. The Demon Fault. Journal and Proceedings, Royal Society of New South Wales. V111.

The New England tablelands seem to be upside down

The geomorphology of the Northern Rivers and New England region can be quite complex. There are many features around the region that have developed as a direct result of the underlying geology. Whether it be the great escarpment, the Ebor Volcano, the backward Clarence River or various other situations, there is always a geological reason for the landscape we see today. In a previous post on the Maybole Volcano near Guyra I quickly mentioned that there is an “inverted topography” which has been created following the deposition of the lava from this volcanic area. Maybole is not isolated in this situation, indeed according to Coenraads & Ollier (1992) much of the basalts in the New England region from Armidale, Walcha, Llangothlin and even places on the other side of the watershed and great dividing range of the Northern Rivers such as Nundle or Inverell show what is technically referred to as relief inversion.

The area around Armidale is actually a good example of the relief inversion, as most hills actually demonstrate the situation nicely. Take, for example, the hill that the University of New England is situated on. The Hill is capped with Cenozoic (Miocene) aged calc-alkaline olivine basalt (part of the Central Volcanic Province) just to the east of the hill (in the paddock below the university carparks) below the level of the lowest basalt flow is a fossil soil horizon, known as a palaeosol. This palaeosol has been affected by lava being deposited on it and has been turned into a material known as silcrete (soil which has been cemented with silica). The old soil was developed on rocks of the Carboniferous aged Sandon Beds. The Sandon Beds outcrop on the lower slopes and in the valleys in and around Armidale but once they were the hills themselves.

The basalts were erupted to the surface the chemical composition of the lava meant that they were quite low in viscosity, that is it was very liquid and consequently the lavas flowed down the valleys that existed at the time. The valleys tended to fill up to varying degrees, leaving only a thin layer of volcanic rock on the existing hill crests of the Sandon Beds or none at all. In the following millions of years the process of erosion would be more effective on the non-volcanic rock and the hills would eventually become incised, turning into gullies and eventually larger valleys. The basalt in the old valleys would remain relatively un-eroded and be become the modern hills.

Evidence of this process can be seen from historic mining of some of the gold around Armidale. The ‘old timers’ would dig under the basalt along ‘deep leads’ which were originally gravel and sand deposits associated with old creeks and rivers. These deep leads had been alluvial gold deposits preserved by the basalt flows. Many of these were mined in the 1800’s and early 1900’s in many areas of the New England district including one quite recently in the Tilbuster area (Ashley & Cook 1988). The silcrete deposits mentioned previously are also examples of the process.

References/bibliography:

*Ashley, P.M. & Cook, N.D.J. 1988. Geology of the Whybatong gold prospect and associated Tertiary deep lead, Puddledock, Armidale District. New England Orogen - Tectonics and Metallogenesis. Conference Papers presented at the University of New England.
*Coenraads, R.R. & Ollier, C.D. 1992. Tectonics and Landforms of the New England Region. 1992 Field Conference - New England District. Geological Society of Australia Queensland Division.

A special volcano on the edge of the Northern Rivers

I have previously mentioned several volcanoes that have existed during the Cenozoic period in and around the Northern Rivers region of the New England. But, it is worth noting that there was once a period of significant volcanism earlier in the Cenozoic which defines the landscape of the Great Dividing Range south of Glen Innes, near the villages of Glencoe (with its excellent pub: The Red Lion Inn) and Ben Lomond. This area is the headwaters of many wild rivers found flowing down the rugged New England escarpment that are tributaries of the Clarence River. On the other side of the divide eventually join the Darling and then Murray River. The Maybole volcano was apparently centred at the modern day and generally unheard of locality, Maybole. It erupted lavas over a large area in every direction including large areas to the west, east and south east.

Maybole lies just on or just outside of the headwaters of the Northern Rivers but none-the-less is worth mentioning because of the extent of volcanic rock that appears to have originated from it. The rocks that have come from the Maybole Volcano are mostly basalt type rocks which were once referred to as the Eastern division of the Central Volcanic Province (Coenraads & Ollier 1992), now referred to as the Maybole Volcanics but still part of the Central Volcanic Province according to Vickery et al (2007). The Maybole Volcanics are comprised of alkali olivine basalt to slightly less silica undersaturated basalt and andesite and reworked volcanic material (epiclastic and volcaniclastic sedimentary rocks) and was erupted around 36-39 million years ago.

Coenraads & Ollier (1992) identified that Maybole was a significant volcano by determining the thickness of basalt that occurred in the region and noticing that at Maybole the thickness was significant at several hundred metres. There are also apparently some dykes and vents that are present. Additionally, they had a close look at drainage patterns and realised that they radiated like the spokes on a bicycle, a classical indication of volcanic geomorphology.

Since Coenraads & Ollier (1992), Vickery et al (2007) has undertaken a major review of the Central Volcanic Province and delineated several constituents of the province. The most significant along this part of the Great Divide is now known as the Maybole Volcanics, obviously directly associated with the Maybole volcano. The age of the Central Volcanic Province including the Maybole Volcanics shows that these rocks are too old to be associated with the Eastern Australian hotspot which formed many of the other major volcanic centres in the region (such as the Focal Peak, Tweed and Ebor Volcanoes). Some time after the end of volcanism from the Maybole Volcano  other volcanoes between about 14-24Ma erupted their lavas over the top of the Maybole Volcanic suite rocks.

Interestingly, it appears that the Maybole Volcanics had affected exactly where the Great Divide was situated because the nature of the existing range was such that the lavas filled the valleys creating thick volcanic piles while the existing hills were only covered with thin layers. This meant redirection of streams and when the rock was eroded the more erodible hills were turned into valleys and the valleys became hills caped with basalt. This is termed an inverted topography. But more about this in another post.

Interestingly, Coenraads & Ollier (1992) have observed that the the great divide has moved over time with some of the old basalt filled valleys showing that they used to flow to the west but with the streams now flowing to the east. It actually appears that the Northern Rivers region is getting bigger!

Red Lion Inn (from Flickr)

PS. Like lots of geologists I like pubs with a good atmosphere and The Red Lion Inn at Glencoe is just such a beautiful place. It is an exceptional location to stop for a meal, especially during the middle of winter while snow is coming down. Alternatively, during autumn while the trees turn bright yellow and red, or during spring while the new leaves are coming out, or even summer! i.e. I recommend it!

References/bibliography:

*Coenraads, R. R., Ollier, C.D. 1992. Tectonics and Landforms of the New England Region in 1992 Field Conference - New England District. Geological Society of Australia Queensland Division.
*Vickery, N. M., Dawson, M.W., Sivell, W.J., Malloch, K.R., Dunlap, W.J. 2007. Cainozoic igneous rocks in the Bingara to Inverell area, northeastern New South Wales. Geological Survey of New South Wales Quarterly Notes v123.

Looking out from the lookout at Point Lookout

The view of the National Park from Point Lookout

One of my favourite places is Point Lookout at the New England National Park between Ebor and Dorrigo. Point Lookout is spectacular for it scenery and feel. On most days you can see the pacific ocean while looking over rugged hills and valleys and I particularly like going there during winter where icicles hang from trees and the waterfalls below the peak are frozen. Point Lookout is nearly 1560metres high which I understand makes it the highest point in northern New South Wales. Like the beauty of the Mount Warning area and Tweed and Brunswick River region, Point lookout owes its attractiveness to the erosion of a large shield volcano.

Point lookout is located on the rim of an escarpment which formed through the erosion of the Cenozoic aged (in this case 19-18 million years) Ebor Volcano and the much older Devonian to Carboniferous (up to ~416Ma) accretionary complex rocks that make up the balance of the New England tablelands. Today, only the north western portions of the lavas (called the Ebor Volcanics) and the central weathered volcanic plug from the Ebor Volcano remain. Research by Ollier (1982) suggested that the central volcanic plug of Ebor Volcano was centred on what is called the crescent which is actually a fairly insignificant looking feature when compared with the rugged valleys today.

It is interesting to note that even though the nearby 23 Million year old Mount Warning (located near and over the Queensland border) is regarded as one of the biggest shield volcanoes in the southern hemisphere, having a height of around 2000 metres before it was eroded, the Ebor volcano was probably a similar size or bigger at its greatest too. It is a bit of a mystery why so little is left of Ebor Volcano when so much remains of the Tweed Volcano/Mount Warning.

The Crescent complex once thought to be Permian (290Ma-250Ma) as recently at the 1970's and was considered part of the intrusives that constitute the New England Batholith. In fact most of the most 'current' geological maps of the area were drawn at this time and so they are incorrect. But since investigations on the radial drainage patterns and geological features by Ollier in the late 1980s followed by dating by Gleadow and Ollier (1987) (which is difficult due to how weathered the Crescent is) and more recent work by Ashley et al (1995) now it is known to be the centre of the Ebor Volcano and aged around 19 Million Years. Ashley et al (1995) also discovered that a nearby basalt called the Doughboy Basalt was around 46 Million years old which is clearly not related to the Ebor volcano but is consistent with other locations where an older Cenozoic basalt is present before the hot spot volcanism that formed the Ebor, Mount Warning and other volcanoes existed.

When I was last at Point Lookout there were several bush walks from long and difficult to short and easy. The most difficult ones take you into the valleys where the rock has been eroded into the older accretionary complex. But even on the short one you can see some interesting 'recent' volcanic rocks. On a section of the walk around the top of the cliffs where security fences are necessary (lest you plummet away!) there is cuttings through the rock. In this rock look closely and you'll see some big crystals within a fine groundmass. This rock is a type of basalt called tholeiite (which means that it has crystalised with a certain geochemical signature) and the crystals are feldspars which is a common rock forming mineral. The feldspars here quite obvious and seem to catch the light at two angles, this feature is called twinning and is characteristic of the calcium rich variety of feldspar called plagioclase. Along the bigger walks below the point dacite can be found as well as basaltic and dacitic breccias at the stunningly beautiful during winter, weeping rock and numerous palaeosols.

The remnant of the shield volcano shows the characteristic radial drainage pattern for volcanic shields but the eroded central areas of the volcano (including the caldera if there was one) drains fairly directly to the east via the Nambucca River. The radially draining creeks and rivers are well known for their waterfalls such as Dangar Falls and Ebor Falls.

The road from Dorrigo to Armidale is not a busy route, it is often missed by many people but I always recommend people visit the New England tablelands because of its beauty and uniqueness in Australia. Point lookout is just off the Waterfall Way which name probably gives you an indication of many of the other attractions. In my opinion, the depths of winter are the best times to visit to get the mood and subtle beauty of the area. I should get back there myself... it has been too long since I was last there.

You may be interested in a self-guided geological tour. Bob and Nancy from Armidale have a wonderful site which includes an excellent (and expanding) range of geological tours including ones of the Northern Rivers Area. Their tour guide on Point Lookout can be accessed from their webpage (very much worth the look) or  directly linked from here.   

References/bibliography:

*Ashley, P.M., Duncan, R.A. & Freebrey, C.A. 1995 Ebor Volcano and the Crescent Complex, northeastern New South Wales: age and geological development. Australian Journal of Earth Sciences V42.
*Gleadow, A.J.W. & Ollier C.D. 1987 The age of gabbro at the Crescent, New South Wales. Australian Journal of Earth Sciences V34.
*Ollier, C.D. 1982 Geomorphology and tectonics of the Dorrigo Plateau, NSW. Australian Journal of Earth Sciences V29.