The geology of the Riverina has several troughs and sedimentary basins. The western Riverina is thought to be the end of the Ballarat and Bendigo geological zone. The eastern part is over the top of the western part of the Lachlan Fold Belt. It is possible that the Riverina has mineral deposits including coal, petroleum, coal seam methane, gypsum, 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 rivers, with more saline grey and brown clays found on rarely flooded areas on the edge of the floodplain. As the Murrumbidgee flows downstream, the water and soil become more saline.