by deposition carried from the Great Dividing Range by streams between 30,000 and 15,000 years ago. The terrain includes rolling hills to the east but then becomes flatter to the west with most of that plain reaching less than above sea level. The western Riverina consists largely of featureless saltbush plain. Landform and hydrology 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. The Riverina is drained by the large Murray-Darling Basin. Rivers and streams in the Riverina generally flow east to west. As well as the Murray, Murrumbidgee and Lachlan, other streams include Billabong Creek and the Edward River, an anabranch of the Murray. Much of the water carried by these streams is diverted. In 2001–2002, 52% of the Murray and Murrumbidgee water runoff was diverted, 77% of which was used for irrigation. Climate The Bureau of Meteorology classify the Riverina in the Hot Dry Zone (with cooler winters) climatic zone. Places in this zone can be very hot in the summer months while in the winter, nights can be considerably cold with cool to mild days. Mean daily maximum temperatures in the Riverina range from in January and in July in Wagga Wagga to in January and in July in Hillston. Under the Köppen climate classification, the region predominantly falls in the hot-summer Mediterranean climate (Csa) zone, although areas in the southwest of the region would feature the semi-arid (BSk) climate and those in the east would have a humid subtropical (Cfa) climate, though still with Mediterranean climate tendencies when it comes to the rainfall pattern. Rainfall levels in the Riverina are generally low with the median annual rainfall over most of the region between , rising to between on the eastern fringe. Because the region is situated on the