The 148ha reserve is about 10km south of Pingelly where the Hotham River crosses the Great Southern Highway. Before European settlement, this area was particularly productive for Noongar people, having freshwater pools teeming with fish, gilgies, birds and animals. It is also the location of the ill-fated Pingelly town dam.
Land clearing for agriculture caused the river and pools to silt and become salty, but the reserve is still an interesting and attractive place.
I found this dolerite hand axe ,which fitted well in my hand, in the bed of the river. I left it in the reserve.
To enter the reserve turn into a side road/ parking bay at the sign just before you cross the Hotham River bridge going to Pingelly. All roads and trails through the reserve are dead end. About 400 metres along Lange Road is an unmarked track to the north. Cars can drive in to an obscure roundabout, which is a good spot to stop to explore for wildflowers. Soon after, the track becomes sandy - only suitable for 4WD vehicles. Keeping to the left the track ends at the Hotham River. Remains of the dam retaining wall is a 450 metre moderately difficult walk through weeds and bush west along the river bank.
Land clearing for agriculture caused the river and pools to silt and become salty, but the reserve is still an interesting and attractive place.
I found this dolerite hand axe ,which fitted well in my hand, in the bed of the river. I left it in the reserve.
To enter the reserve turn into a side road/ parking bay at the sign just before you cross the Hotham River bridge going to Pingelly. All roads and trails through the reserve are dead end. About 400 metres along Lange Road is an unmarked track to the north. Cars can drive in to an obscure roundabout, which is a good spot to stop to explore for wildflowers. Soon after, the track becomes sandy - only suitable for 4WD vehicles. Keeping to the left the track ends at the Hotham River. Remains of the dam retaining wall is a 450 metre moderately difficult walk through weeds and bush west along the river bank.
This remarkable reserve has three main landscape types
- 1 The Hotham River, comprising a series of channels where the river has changed course.
- 2 Adjoining sand dunes to the south.
- 3 An ephemeral pool adjoining the dunes then an upward slope of woodland, balgas and scrub overlying sand over gravel or clay and gravel soils.
To the east of the reserve is a large dune-surrounded saline wetland. Banksia sand dunes adjoining the river are uncommon in this area. Adjoining examples are Kokeby and the Yenyenning lakes to the north, Lake Yealering to the east, and Lake Toolibin to the southeast. Ancient land movements blocked and diverted ancient rivers to create lakes and wetlands at these places.
This wetland marks the junction of the Hotham River South, Calcoran Brook, and Hotham River North on the northern edge of the Hotham River catchment. North and South Hotham rivers make a U-turn at the reserve to flow west/southwest, and there are unusual ephemeral ponds on the upside of dunes.
So, what caused the Hotham South River to take a sharp turn here and why are there dunes and wetlands? My simplified explanation follows.
This wetland marks the junction of the Hotham River South, Calcoran Brook, and Hotham River North on the northern edge of the Hotham River catchment. North and South Hotham rivers make a U-turn at the reserve to flow west/southwest, and there are unusual ephemeral ponds on the upside of dunes.
So, what caused the Hotham South River to take a sharp turn here and why are there dunes and wetlands? My simplified explanation follows.
What created this landscape?
This region is underlain by a stable piece of continental rock called the Yilgarn Craton, which is mainly granite and gneiss, some of the world's oldest (over 3 billion years) rocks. As the craton formed, then joined and separated from others in supercontinent cycles, the bedrock cracked. These cracks are faults, and dolerite dykes (where magma beneath the continent has squirted up into the gaps. This area has more dykes than usual.
About 540 million years ago Australia was connected to the supercontinent Gondwana by Greater India to the west, and Antarctica to the south. Mountains associated with these connections eroded away to leave a subdued landscape. In this area, land sloped gently to the coast, but waterways often deviated along underground faults and dykes.
India gradually separated from WA creating a rift valley (the Swan Coastal Plain), which received sandy sediments via west flowing rivers from a divide around Corrigin.
This region is underlain by a stable piece of continental rock called the Yilgarn Craton, which is mainly granite and gneiss, some of the world's oldest (over 3 billion years) rocks. As the craton formed, then joined and separated from others in supercontinent cycles, the bedrock cracked. These cracks are faults, and dolerite dykes (where magma beneath the continent has squirted up into the gaps. This area has more dykes than usual.
About 540 million years ago Australia was connected to the supercontinent Gondwana by Greater India to the west, and Antarctica to the south. Mountains associated with these connections eroded away to leave a subdued landscape. In this area, land sloped gently to the coast, but waterways often deviated along underground faults and dykes.
India gradually separated from WA creating a rift valley (the Swan Coastal Plain), which received sandy sediments via west flowing rivers from a divide around Corrigin.
Australia as part of Gondwana 300 million years ago. Left image courtesy P. Lane.
66 million years ago the Darling Range gradually rose up as a range of ridges east of the Darling Fault. An associated valley on the eastern edge of the range shows as a line of waterways roughly following the Great Southern Highway from Cuballing (Hotham River South), then up to Dalwallinu (Avon and Mortlock Rivers).
This and a possible east-west uplift just south of Pingelly, blocked rivers upstream of the reserve to create a lake. During periodic geological climate changes the lake filled and dried. In arid climate phases, sand blown from the dry lakebed formed dunes that were colonised by Banksias.
Eventually the river cut through a rise on the western side of the lake leaving the dunes and wetlands that exist now.
This and a possible east-west uplift just south of Pingelly, blocked rivers upstream of the reserve to create a lake. During periodic geological climate changes the lake filled and dried. In arid climate phases, sand blown from the dry lakebed formed dunes that were colonised by Banksias.
Eventually the river cut through a rise on the western side of the lake leaving the dunes and wetlands that exist now.
Relief map. Note north-south Hotham River and parallel ridge to the west, which once blocked water flow to create the wetland
The last feature is the seasonal pond on the upside of dunes in the reserve. Why would sandy dunes hold back water?
The answer is revealed in a radiometrics map. The red colouring in the image indicates a large dolerite dyke underneath the river channel and dune area. Dolerite weathers to reddish clay soils. In winter, subsurface water flowing down from sandier soils to the south meets less permeable dolerite clay and rises to the surface – hence a pond adjoining the dunes.
Dolerite dykes are frequently found on the downside of salt areas, and may have also influenced the river direction.
The answer is revealed in a radiometrics map. The red colouring in the image indicates a large dolerite dyke underneath the river channel and dune area. Dolerite weathers to reddish clay soils. In winter, subsurface water flowing down from sandier soils to the south meets less permeable dolerite clay and rises to the surface – hence a pond adjoining the dunes.
Dolerite dykes are frequently found on the downside of salt areas, and may have also influenced the river direction.
Diagonal reddish dolerite dyke in line with the river with ephemeral ponds on either side. Dull green shade marks sandy gravel soil
Exploring the Reserve
Despite bring mined for sand and gravel and once having tracks associated with the pump and reservoir, there is a diverse range of lanscapes and vegetation which is mostly in good condition. I thoroughly enjoyed walking through the bush, but inexperienced walkers could become lost, and as in all our bush, kangaroo ticks may be a problem if one walks through vegetation in late spring, summer and autumn.
Orchid lovers can enjoy the range of spider and other orchids by exploring open land adjoining Lange Road.
Note that all bush tracks are sandy and potentially boggy. Only drive cars into area 2 to where there is a turn around spot. If using a 4WD please drive slowly and sparingly as this country is easily destroyed. Note, there is dieback in bush to the east of the reserve. Do not drive off tracks.
Despite bring mined for sand and gravel and once having tracks associated with the pump and reservoir, there is a diverse range of lanscapes and vegetation which is mostly in good condition. I thoroughly enjoyed walking through the bush, but inexperienced walkers could become lost, and as in all our bush, kangaroo ticks may be a problem if one walks through vegetation in late spring, summer and autumn.
Orchid lovers can enjoy the range of spider and other orchids by exploring open land adjoining Lange Road.
Note that all bush tracks are sandy and potentially boggy. Only drive cars into area 2 to where there is a turn around spot. If using a 4WD please drive slowly and sparingly as this country is easily destroyed. Note, there is dieback in bush to the east of the reserve. Do not drive off tracks.
Area 1 gives a good cross section of the gentle slope down to the dunes. Mostly it is fairly easy and attractive walking country. Apart from a couple of small breakaways, soils are mostly sand over clay/gravel underlain at depth by granite or dolerite bedrock. Vegetation varies according to bedrock, with thicker bush and more orchids/other flowers on paler sandy soils.
 yellow sand slope |  Red sand sedge slope |  Gravelly spur |
You can also often tell soil types by change in ant hill colour as you walk.There is a small group of Caladenia roeii clown orchids on the upslope of the road between the two low rises.
 Pale sand |  Red sand |  Clown Orchid Claldenia roeii |
Area 2. Drive down the unmarked track and park at the (indistinct) roundabout.
2a is attractive open woodland on the upper side, which has a fine display of Chapmans Spider Orchids in September
2a is attractive open woodland on the upper side, which has a fine display of Chapmans Spider Orchids in September
 |  Caladenia chapmanii |  |
2b is a short walk west from the parking loop. The ephemeral pond bounded by a line of Melaleuca phoenicia shrubs (ex Callistomen phoenicous) then dunes, is a geological oddity. It was once fresh, but has become slightly saline due to salt released from the subsoil of cleared land at the top of the slope. Most winters it hosts wetland plants, algae, and aquatic invertebrates.
 July |  Draped algae as the pond dries |  Early September |
Few Caladenia discoidea on dunes 2c is a band of low sand dunes and interdunal hollows as you walk towards the river. Landscape and vegetation varies depending on depth of sand, with many different types of shrubland, but there are few orchids. Dunes consist of Banksia prionotes acorn banksia, Banksia attenuata candlestick banksia, and Allocasuarina huegeliana (rock sheoak) with little understorey.
Interdunal areas are shrublands which vary greatly depending on the depth of sand over clay, and moisture availablity. They are attractive in late spring due to the range of flowering species, which include some that are locally rare (e.g. Calytrix acutifolia, Grevillea anethifolia).
This has been a dry spring with fewer flowers than normal.
Interdunal areas are shrublands which vary greatly depending on the depth of sand over clay, and moisture availablity. They are attractive in late spring due to the range of flowering species, which include some that are locally rare (e.g. Calytrix acutifolia, Grevillea anethifolia).
This has been a dry spring with fewer flowers than normal.
 Banksia dune |  Interdune |  Interdune |
Remnants of the weir Area 3 River.
The river area consists of the Hotham River, associated dry channels and fringing vegetation. The fringing vegetation is very weedy with lots of introduced grasses and Bridal Creeper. The old dam is about 450 metres west of the point where the track ends. LIttle remains apart from a line of posts, and to reach it is a scramble through uneven weedy land unless the river is dry and one can walk along the river bed.
The dam and it's history is contained in this blog.
The river area consists of the Hotham River, associated dry channels and fringing vegetation. The fringing vegetation is very weedy with lots of introduced grasses and Bridal Creeper. The old dam is about 450 metres west of the point where the track ends. LIttle remains apart from a line of posts, and to reach it is a scramble through uneven weedy land unless the river is dry and one can walk along the river bed.
The dam and it's history is contained in this blog.
Hotham River zone in the reserve
Area 4. This is a narrow strip of land containing a drain going between the highway and Power Street to the river. Lots of green spider orchids and flowering shrubs in September.
 Grevillea anethifolia |  Unusual Caladenia falcata |  Dampiera lavendulaceae |