2.1.2 Hills, valley slopes and plains on non-granitic Palaeozoic rock (Concongella Hills, Mount Dryden)

Lower in the topographic sequence than the ridges, escarpments and mountains of the Midlands (dissected uplands) are the neighbouring hills, valley slopes and plains of the upper Wimmera catchment. These eroding landscapes occur from Mount Dryden in the west to the fringing hills of the Pyrenees Ranges in the east. Comprising strike ridges and valleys, (complexes of hills and low hills intermixed with surrounding rises and plains) to rises and a broken chain of low hills in the Mount William Creek catchment, the undulating to steep topography of these landscapes provide a fundamental link between the mountainous terrain of the Pyrenees Ranges and Ararat Hills to the alluvial drainage plains of the Wimmera River and Mount William Creek.

These landscapes are more subdued than those of the Pyrenees and Ararat Hills and are distributed as isolated hills in the west compared to the larger coherent landscapes in the south and east of the upper Wimmera catchment. Slopes can be variable from steep hill slopes to lower slopes and footslopes, however slope segments are often considerably longer than those of the Pyrenees Ranges. Stream channel drainage is quite varied reflecting the suite of landform patterns within the region.

The Mount Dryden Hills are a sequence of isolated low hills to the east of the Grampians Ranges. Trending north-westerly, these hills are 60–100 m higher the surrounding alluvial plains. Slopes are steep with the topography of these hills being more subdued in the south where slopes tend to be moderately to gently inclined. Mount Dryden is the highest (382 m) and largest outcrop, and due to the isolated nature of outcrops has radial drainage patterns that feed into Mount William Creek. In the upper reaches of Mount Cole Creek and the Wimmera River, low hills occur as isolated outcrops adjacent to neighbouring granite plutons. Slopes here are moderate to gentle with little significant relief.

The Concongella Hills are surrounded by a suite of landforms that underlie these topographically prominent features. Low hills, rises, plains and drainage depressions are common within this landscape complex that is bound to the east by the Wimmera River/Mount Cole Creek and by Mount William Creek in the west. Hillslopes are steep to moderately inclined with the remaining slopes of the landscape gently inclined. Drainage is dendritic away from the hills where radial drainage is dominant.

Extensions of the Pyrenees Ranges in the east of the upper Wimmera catchment include hills east of Joel South. Here upper slopes are steep with long gently inclined lower slopes that converge into footslopes and rises that line Wattle Creek and Howard Creek.

The Mount Dryden Hills are a fault-controlled belt of volcanic rocks (calc-alkaline andesitic and dacitic lava, intrusives and fine grained volcaniclastics) striking north-north-westerly (Cayley & Taylor 2001). Cainozoic ferruginised ironstone flank many slopes of these hills.

Further in the east, the landscapes are composed of sedimentary rocks that have been folded and faulted in post-Ordovician times. Metasediments that have experienced low grade regional metamorphism can be observed in the subdued strike ridges to undulating hills of the Concongella Hills and surrounding landforms. Weathering is variable with pallid kaolinitic profiles tending to be deeper on areas of lower relative relief than topographically pronounced landforms are (e.g. mountains, escarpments). Palaeogene remnants (ferruginous duricrusts) are common on hillslopes and crests of low hills/rises.

Red texture contrast soils (Chromosols) that tend to be sodic (Sodosols) in lower topographic positions have developed on hills, valley slopes and plains. Surfaces are lightly textured well structured soils that have a sharp contrast with the medium to heavy subsoils that have vastly slower infiltration rates. While slightly acidic at the surface, they become alkaline at depth with profiles on lower slopes having deeper profiles than steeper upper slopes. Variable amounts of coarse weathered bedrock fragments and quartz occur throughout the profile.

Vegetation communities reflect variation in climate, aspect, geology and morphology. The Mount Dryden Hills have Heathy Woodland, Plains Grassy Woodland and Shrubby Woodland found on well drained soils. Vegetation communities such as Creekline Grassy Woodland and Seasonally Inundated Shrubby Woodland are found on lower slopes and drainage depressions.

The Concongella Hills and Rhymney low hills area has remnant vegetation dominated by forest and woodland areas. The main vegetation communities include Heathy Dry Forest, Grassy Dry Forest, Grassy Woodland, Plains Grassy Woodland, Alluvial Terraces Herb-rich Woodland and Heathy Woodland. Creekline Grassy Woodland occurs in the lowest positions of these landscapes. Granitic Hills Woodland can also be located on these non-granitic landforms.

Adjoining the Pyrenees Ranges, remnant forest and woodland areas dominate vegetation. Heathy Dry Forest, Grassy Forest, Box Ironbark Forest and Grassy Dry Forest are found in exposed areas, Hillcrest Herb-rich Woodland, Grassy Woodland, Creekline Grassy Woodland and Plains Woodland found in more sheltered areas, or in areas at higher altitudes.
The Concongella Hills are an extremely vulnerable landscape to erosion and dryland salinity. Gully and tunnel erosion, and sheet and rill erosion are common on moderate to steep slopes especially where remnant vegetation has been removed for grazing purposes. Landslides and mud flows are likely where steep to very steep slopes occur, especially on lower peripheral landscapes within the Pyrenees Ranges.

Salinity processes within the metasediments of the upper catchment are driven by local to intermediate groundwater flow systems within fractured bedrock. Groundwater processes operate within the top 50–100 m of the landscape where groundwater discharge often occurs at the break-of-slope. Bedrock of lower relief partially discharges within the upper catchment with salinity levels derived from vast salt stores varied between 3000 mg/l to 12 000 mg/l (WCMA 2005).

Soil-landform unit	Unit description	Area (km²)
Concongella Hills	Hills	69
Elmhurst footslopes	Hillslopes and footslopes	8
Joel South hills	Hills	43
Kanya hills	Low hills	13
Landsborough footslopes	Plains and footslopes	115
Mount Dryden metamorphic hills	Metamorphic hills	21
Navarre foothills	Foothills	117
Rhymney hills	Undulating low hills	183
Surridge foothills	Footslopes and foothills	58

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