|This unit is located in western Victoria, clearly bounded by the Big Desert to the north and the little Desert to the south. The South Australian border is the artificial western boundary and the Wimmera River Valley (Lowan Salt Valley) is the eastern boundary. Similar terrain is found to the south of the Little Desert.|
This unit is dominated by a series of parallel and sub-parallel ridges orientated NNW/SSE, interspersed with similarly aligned valleys or swales. This pattern is still discernible in the siliceous dunefield units (5.2) to the north and south. This landform pattern is at its most distinct in this unit with the relative relief of the ridges ranging from 10 to 60 m. The major ridges (Diapur/LawloitRange/Propodollah) have an amplitude of about 5km with slopes of up to 8%, while the smaller ridges have an amplitude of 2 km and slopes up to 5%. The larger ridges have a complex of components including elevated swales/valleys.
The intervening valley floors may extend to plains in the west and nearer the eastern boundary. These valley floors are dominated by lagoonal deposits, which can be quite shallow as well as the occasional swamp. There is the occasional sandy dune.
The ridges consist Parilla Sand (Tpp), ferruginised at the surface which are exposed on the larger ridges, while Woorinen Formation (Qw), calcareous sandy clay regolith material (parna) covers most of the smaller ridges. Reworking of the Parilla Sand crests has resulted in a younger unconsolidated silceous sand (Lowan Sand; Ql) on the crests and on the valley floors/plains. The valley floors have younger lagoonal deposits(Qrs) consisting of expansive (cracking) dark organic clays, which may be quite shallow at their edges.