|Below 40 m elevation in the Raak and Noora Depressions, and 60 m in the Tyrrell Depression, landscapes have been modified by groundwater discharge. Blanchetown Clay has been salinised, then deflated to form landform complexes known as “boinkas”. These are mostly large but in some districts they are scattered and only 1-2 km across, particularly to the north of Lake Timboram and to the south and east of Ouyen.|
Salinas occupy the lowest sites where salts and gypsum have accumulated in muds derived from dust and lacustrine deposits. Salinas occupy most of the lake beds in the Tyrrell Depression, and about half on the Raak Plain and the Noora boinkas. However they are infrequent in the boinkas to the north of Cowangie and Underbool, except in the Pink Lakes area.
Plains with halophytic shrubs occur where depth to groundwater is a little greater. The very salt-tolerant Samphire (Halosarcia spp.) fringes the salinas and occupies the lowest levels to the north of Cowangie and Underbool when salinas are absent. At yet higher elevations above the water table there are Saltbush (Atriplex spp.) shrublands which often alternate with Samphire in a complex pattern.
Raised sandplains are widespread on the Raak Plain where they alternate with north west - south east ridges, salinas and plains with halophytic shrubs. The soils are reddish-yellow sands with reddish clayey sand subsoils, apparently derived from sand dunes blown in from the west. In the north-west corner of the Raak Plain there is a remnant of unit 5.1.1 in which linear dunes are dominant. Subsequent lake-full conditions have reworked the sands to produce the raised sandplains with smooth boundaries. Grasslands predominate and these were grazed by livestock for many years. There are fringing trees such as pine, belah and mallee eucalypts on the red sands, particularly along the eastern margin of the plain.