The Mallee covers the most northwesterly part of Victoria, bounded by the South Australian and New South Wales borders. Definitions of the south-eastern boundary vary, however, all are based on the historic Victorian distribution of mallee eucalypts. These trees dominate the surviving vegetation through most of Mallee, (except for swamps and areas along waterways, and very rare stands of casuarina). Its biggest settlements are Mildura and Swan Hill. At the 2011 census, the four local government areas (LGAs) that are usually thought to define the district had a combined population of . The area of these same four LGAs is . There is an adjacent area also once covered with mallee scrub called "the Mallee" in South Australia, which is alternatively called the Murray Mallee. Geography and climate The Mallee is, for all practical purposes, completely flat and very low-lying: in fact, for long geological periods the whole region has been inundated by the ocean. Most of the Mallee consists of sand dunes that have been deposited as a result of movement of sand from the interior of Australia during arid glacial periods of the Quaternary. The soils are generally very infertile and sandy: the better ones on more stabilised sand dunes in the east are slightly loamy and pink to light brown and have been able to support wheat and barley growing as a result of the development of superphosphate and other fertilisers. In the west, the soils are unconsolidated sands, much less alkaline than in the east, and not generally able to support any grain cropping. The Mallee has no surface drainage: the native vegetation has so high a rooting density that the rainfall of most years is easily absorbed and the porous sandy soils mean that any excess in an exceptionally wet year will recharge groundwater supplies which tend to be highly saline. Flow from the Wimmera River to the south supplies Lake Hindmarsh and, very occasionally (in 1918, 1956 and 1975), overflows to the north. The Murray River is, thus, the only source of fresh water for the region and is consequently overburdened by intensive irrigation. As of 2019, 61% of the area utilizes drip irrigation. The climate of the Mallee is the hottest and driest in Victoria owing to its inland location. Rainfall is usually only produced by the most vigorous frontal systems or by occasional penetration of tropical air in the summer. Average annual