17°S 145°E Thornborough – Queensland by Degrees
Location: This confluence point is 2.64 km west of the Dimbulah - Mt Mulligan Road and was reached on foot from the road using GPS to accurately locate the point. The point lies on The Pinnacles station and is within the Tablelands Regional Council area. The closest settlement is Dimbulah, 20 km to the south-south- east.
Squatter pigeon near the confluence point (Ken Granger, 2008)
The Landscape: The point has an elevation of 492 m ASL and is located in rounded hilly country of Devonian age (410 - 354 million years) fine-grained greywacke of the Hodgkinson sedimentary formation. The soil is shallow and stony. It supports a vegetation of low open eucalypt woodland dominated by bloodwoods and ironbarks to 10 m in height and with a ground cover of tussocky grasses and shrubs. The ground cover can be difficult to push through if it has remained unburnt for some time.
Land use around the point is cattle grazing - a large cattle yard is located by the Dimbulah - Mt Mulligan road a few kilometres from the point.
Fauna noted in the vicinity of the confluence point include macropods - mainly Wallaroos and Eastern Grey Kangaroos- as well as cattle and brumbies. A wide range of reptiles are also in the area including the dangerous King Brown and Eastern Brown snakes and the large Sand Goanna. Bird life is well represented with several parrot species including the Red Tailed Black Cockatoo, various pigeon species (the Squatter Pigeon is fairly common), honeyeaters and raptors such as the Black Kite.
Point information and photos: Kev Teys, Bruce Urquhart, John and Mary Nowill, 2008; Ken and Judy Granger also got to within 3 km of the point on the Dimbulah - Mt Mulligan road, 2008.
WITHIN THE DEGREE SQUARE
The Country: The country within this degree square is probably the most diverse and complex of all of the 185 degree squares within Queensland. It extends from the coast just to the south of Port Douglas, through the wet tropics of the Great Dividing Range, the volcanic landscapes of the Atherton Tablelands, the irrigation lands around Mareeba and Dimbulah to the savannah sand plains around Chillagoe. Elevations range from sea level to around 1300 m ASL near Atherton and 1224 m ASL on Mt Lewis to the east of Mt Carbine. There are several high points in the Great Dividing Range within the square that are over 1000 m ASL. Much of the area west of the Divide is above 500 m ASL. The lowest elevation is along the Mitchell River at around 200 m ASL.
Most of the coast-flowing rivers such as the Mossman, Barron, Mulgrave and North Johnstone are deeply incised as they flow off the range and most have significant waterfalls and gorges. The coastal scarp is very steep and rugged. Apart from the Mt Carbine granite, the bulk of the Great Dividing Range is composed of sedimentary rocks of Devonian age (410 to 354 million years) such as mudstone and greywacke. The intruded granite around Mt Carbine is of Permian age (298 to 251 million years). The alluvium eroded from these mountains has produced a very fertile coastal plain.
This is in marked contrast to the Atherton Tablelands with their wide rolling plains, deeply incised edges and remnants of Pliocene-Pleistocene age (less than 5 million years) volcanic activity. The most prominent volcanic relic within the degree square is the Mt Hypipamee Crater. This explosion pipe (or diatreme) is a circular crater about 60 m in diameter and 60 m from the crest to water level - the pipe extends a further 85 m below the surface before bending under to an unknown depth. The more familiar volcanic landscape features such as the crater likes of Lake Eacham and Lake Barrine are just to the east of the degree square boundary.
The rivers that flow towards the Gulf of Carpentaria, such as the Mitchell, Hodgkinson and Walsh, are less deeply entrenched. The landscape is less rugged and the general relief is significantly lower than along the eastern side of the Divide.
The underlying geology is very complex. The most ancient rocks are of early Silurian to Early Devonian (434 to 384 million years) in the Chillagoe Formation which is found in a few small patches in the west and south-west of the square. These are sandstones, siltstones, mudstones and limestones that are typically surrounded by extensive sand plains. The sand plains are fairly flat though some spectacular remnant outcrops of the ancient rocks, such as the limestone pinnacles around Chillagoe itself, tend to dominate the landscape. The Devonian limestone within the Chillagoe-Mungana National Park is famous for its caves and limestone karst pinnacles.
Chillagoe karst limestone and sand plain country (Ken Granger, 2008)
'Crystal Madonna' and other formations in the Donna Caves, Chillagoe-Mungana National Park (Ken Granger, 2008)
Typical Hodgkinson Basin country with the Mt Mulligan massif in the background (Ken Granger, 2008)
Part of the Chillagoe limestone has been metamorphosed to a very fine-grain marble that is now being mined.
More than a quarter of the degree square is composed of Devonian age greywacke, as found at the confluence point. The basins of both the Mitchell and Hodgkinson Rivers are based on this formation. It gives rise to generally low relief of rolling hills. Standing out from the southern side of the Hodgkinson Basin is the Triassic age (251 to 141 million years) sandstone massif of Mt Mulligan. This rises more than 500 m above the surrounding country.
The next largest area is that occupied by lavas of Early Permian age (298 to 270 million years) through which the Walsh River flows. Igneous rocks also make up much of the country in the south of the degree square. Much of this is Late Carboniferous age (325 to 298 million years) granite that produces a steeper terrain than that of the older greywacke formations. The country between Atherton and Herberton is typical of this granite country.
Vegetation across the square is also very diverse. Medium height (to 30 m) tropical rainforest is found along the eastern scarps of the Great Dividing Range and on the upper slopes of the Divide. A very large number of species are found in the canopy layer making this one of the richest forest habitats in Australia. Over 2000 species of trees, shrubs and vines have been recorded in these forests. The tallest species such as Hoop Pine (Araucaria cunninghamiana), Bunya Pine (Araucaria bidwillii), Kauri Pine (Agathus robusta and A. microstachya), Black Bean (Castanospermum australe), Black Walnut (Endiandra palmerstonii), Red Cedar (Toona ciliata) and Flooded Gum (Eucalyptus grandis) were all sought after for commercial logging before the Wet Tropics World Heritage Area was proclaimed and logging ceased. Various species of Ficus including the massive Strangler Fig (Ficus watkinsiana) are also prominent. The understory of saplings, seedlings, palms, tree ferns, vines and herbs such as gingers can be very dense. Some of the rainforest plants are hazardous. The most common of these is the Stinging Tree (Dendrocnide moroides), the leaves of which have fine silica hairs that can inflict severe pain if they are brushed against; and the Wait-a-While vine (Calamus moti) and its relatives, Hairy Mary (C. australis) and Vicious Hairy Mary (C. radicalis) that have very sharp hooks and spines that can inflict painful cuts and tears if brushed against.
On the western side of the Divide the vegetation becomes progressively more open, canopy height becomes lower, the species composition becomes far less diverse and the understory changes to tussocky grasses. In the area immediately west of the Divide tree height is around 30 m and the canopy is mostly closed. On the hilly country from Herberton to Chillagoe the bush is medium height open woodland of eucalypts such as Narrow-leaved Ironbark (Eucalyptus crebra), White Mahogany (E. acmenoides) and Cullen's Ironbark (E. cullenii). Other species include Rose Sheoak (Allocasuarina torulosa), Turpentine (Syncarpia glomulifera) and Cyprus Pine (Callitris intratropica). In the karst areas near Chillagoe the deciduous Broad Leaved Bottletree (Brachychiton australis) and Kurrajong (Brachychiton chillagoensis) are features in the landscape.
The lower country of the Walsh, Hodgkinson and Mitchell River catchments carry a low open eucalypt savannah.
Savannah near Kingsborough (Ken Granger, 2008)
As with the vegetation, the wildlife of the area is also very diverse. In the rainforest areas tree-dwelling mammals such as the Lumholtz's Tree Kangaroos, Feathertail Gliders, Sugar Gliders, Striped Possums and Brushtail Possums make their homes along with a range of both fruit and insect-eating bats. On the forest floor can be found Swamp Wallabies and Red Legged Pademelons together with a wide range of native rodents. In the drier country to the west of the Divide the Wallaroo, Eastern Grey Kangaroo, Agile Wallaby and Northern Nailtail Wallaby are more common. Several species of bats including Bent-wing and Horseshoe Bats are found in the Chillagoe caves. Dingos are found in all habitats.
The area has a diverse and spectacular bird fauna. Some 300 bird species have been recorded in the Julatten area with habitats ranging from wetlands of Lake Mitchell to the rainforests of Mt Lewis. Amongst these are the migratory Buff-breasted Paradise Kingfisher and its relative, the Little Kingfisher of the rainforest; the Blue-faced Parrot-Finch of the rainforest fringe; the ground-feeding Cassowary, Orange-footed Scrubfowl and Bush Stone-curlew; and a wide range of honeyeaters, raptors and pigeons. Around Mareeba and Atherton seasonally large flocks of Red Tailed Black Cockatoos, Brolgas and Sarus Cranes are common, whilst in the drier interior Wedge-tailed Eagles, Emus and Bustards stand out.
The rainforest is also home to a large number of butterfly and beetle species. Of the butterflies, the Ulysses Swallowtail and the Cairns Birdwing are amongst the most spectacular.
The Climate: The diversity of the degree square's landscape is to some extent a reflection of its climatic range. The climate ranges from tropical monsoonal along the coast to tropical savannah on the west of the range and subtropical with a distinctly dry winter further west. The climatic averages for Cairns Airport (just outside the square to the east) and Mareeba (on the Tableland) provide a contrast. Unfortunately the BoM web site does not include data for Chillagoe in the extreme west of the square.
Cairns Airport (site 031011) 1941-2008 (elevation 2 m ASL)
Mareeba QWRC (site 031066) 1952-2008 (elevation 400 m ASL)
The highest temperature ever recorded in Cairns was 40.5°C in December 1990 while the lowest temperature was 6.2°C in June 1946. Rainfall also varies greatly. The highest total of 3148.8 mm was recorded in 2000 and the lowest total of 721 mm in 2002. In January 1981 the monthly total was 1417.4 mm.
The extremes at Mareeba, some 400 m higher in elevation and only 38 km inland, but on the western side of the Great Dividing Range, show a highest maximum of 40.6°C in November 1990, a record low of 0.4°C in June 1963; a highest rainfall of 1730.2 mm in 1974 and a lowest total of 388.8 mm in 1966. Dimbulah, a further 35 km to the west has an average rainfall of only 783.8 mm, a highest rainfall of 1876.8 mm in 1974 and a lowest recorded rainfall of 326.0 mm in 1993. Towards the western edge of the square the average annual rainfall is probably as low as 600.0 mm per annum.