Devonian rhyolite is the major geological material forming this unit. It is deeply weathered and outcrops, mainly on the dissected slopes around Rocklands Reservoir. The landform is predominantly undulating rises dissected by numerous drainage depressions. On areas of lower relief, strong texture contrast soils with a ferric horizon and a strongly acidic subsoil (Kurosols) are found, although less acidic subsoils also occur (Chromosols). The rises and low hills tend to have Ferric Chromosols. The subsoils are rarely sodic.
Plate 48 & 49 Remnant vegetation near Rocklands Reservoir, west of Mooralla (Plate 48) and the
Nigretta Falls located between Hamilton and Wannon with exposed Rocklands Rhyolite (Plate 49).