 The geology of the Riverina comprises several troughs and sedimentary basins . The western Riverina is presumed to be a continuation of the Ballarat and Bendigo geological zone while eastern sections are underlain by western portions of the Lachlan Fold Belt . There is potential for the Riverina to host several mineral deposit types including coal , petroleum , coal seam methane , gypsum , orogenic gold , Cobar style polymetallic systems , heavy mineral sands and possibly diamonds in these fold belt rocks and basins . Riverina soils are generally sandy along the river channels , with more saline grey and brown clays found on rarely flooded areas on the perimeter of the floodplain . As the Murrumbidgee passes downstream , the water and soil become more saline . 
