2.1.3 Ridges, escarpments, mountains on granitic Palaeozoic rock (Langi Ghiran, western Black Range - Mount Sugarloaf)

Ridges, escarpments and mountains of granitic origin can be found within the highest reaches of the Wimmera River and Mount Cole Creek. These granitic plutons are scattered throughout the Midlands and form prominent hills and mountains that rise above their surrounding metamorphic aureoles and other areas of country rock (Joyce et al. 2003).

The positive relief plutons such as Langi Ghiran (922 m), formerly known as Larne Gerin (Hills 1975), Ben Nevis (879 m) and the western Black Range (559 m) form prominent hills and mountains that rise above surrounding metamorphic aureoles and alluvial drainage systems. Tors and boulders of granite and larger granite outcrops represent whalebacks on their flanks (Cayley & MacDonald 1995). The slabby cliffs that rise above rock overhangs (whaleback) of Ben Nevis are the largest developed in Victoria.

Significant plateau remnants are preserved on the Mount Buangor Range with very minor segments preserved on Langi Ghiran. The plateaux have low gradients with moderate to gently inclined slopes with streams that drain these surfaces. Margins of the plateaux are steep to very steep with radial drainage away from these plutons.

Granitic landscapes within the WCMA region comprise granite plutons belonging to three suites (Mount Cole, Glenlogie and Ararat) that approximately intruded 390 million years ago (White & Chappell 1983) as part of the Lachlan Fold Belt plutonism events. These granitic masses that have been stripped of ancient palaeosurface materials have left pronounced topographic features (plateaux) on steep to precipitous slopes. Plateau remnants, considered to be early Mesozoic in age (Hills 1940; King 1959), are the oldest surviving geomorphological features of the WCMA region.

The Langi Ghrian Granite, Ben Nevis Granite and Mount Cole Adamellite all form part of the Mount Cole Suite within the Stawell Province of the Whitelaw Terrane. Regolith is relatively shallow to nonexistent on steeper slopes with deeper profiles occupying plateau cappings. The Black Ranges are derived from the Stawell Granite where little regolith exists and is dominated by rocky outcrop.

The granites generally have developed sandy soils, with profiles varying from uniform or weakly gradational sands (Kandosols) to strongly texture contrast ferruginised (‘buckshot’ or iron pan) soils (Chromosols and Kurosols). The yellow texture contrast soils are strongly acidic at the surface, becoming slightly acidic or neutral at depth. Weakly structured surfaces overlie a massive horizon with variable amounts of coarse quartz fragments. Subsoils are medium to heavy clays often with conspicuous mottling. Total soil depth is variable depending upon differential weathering but generally increase with decrease in topographic position.

Vegetation is dominated on the Mount Cole Granitic Suite by Grassy Dry Forest. Other vegetation communities present include Herb-rich Foothill Forest, Hills Herb-rich Woodland, Grassy Woodland and Alluvial Terraces Herb-rich Woodland/Plains Grassy Woodland Complex. The Black Range has a similar variety of remnant vegetation communities, however it is more exposed to prevailing winds from the north, south and west. Riparian Scrub, Shallow Sands Woodland, Creekline Grassy Woodland and Heathy Woodland are variants.

Groundwater migrates through aquifers comprising either abundant colluvium found on slopes or underlying weathered and fractured/jointed bedrock. Shallow perched groundwater through lateral flow migrates downslope and discharges at the break-of-slope or feeds into basal aquifers that underlie adjacent valleys (WCMA 2005).

The eroding granitic slopes are extremely vulnerable to extreme rainfall events in the form of sheet and rill erosion. Landslides and mud flows can eventuate where extreme rainfall events are coupled with land clearance and steep slopes. Landslips and mudflows occur where saturated soils fail.

Soil-landform unit	Unit description	Area (km²)
Langi Ghiran ranges	Granitic mountains	121
Sugarloaf granite hills	Granitic hills	26

Figure 5 Eastern Black Range, south of Stawell

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