 In general , the Riverina is an alluvial plain formed 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 200 metres ( 660 ft ) above sea level . The western Riverina consists largely of featureless saltbush plain . 
