Northern Myall Plains (Environmental Region 4.4)
This region consists of seven environmental associations. It lies north of and is geomorphologically similar to region 4.3 but has been separated from it because of a distinct change in vegetation from mallee to myall (Acacia sowdenii), and in land use from wheat cultivation to extensive livestock grazing. The area mainly comprises undulating plains with calcrete development and with reddish calcareous earths. Dunes and sand sheets occur locally, as do salt lakes and flats. Occasional extensive hogback ridges such as the Middleback Range form prominent landmarks. Red duplex soils are developed on the footslopes of the hills and ridges. Myall occurs throughout the region, with an understory of bluebush (Maireana spp.) or saltbush (Atriplex vesicaria). The coastal zone is characterized by gently sloping fans and outwash plains, but some of which are traversed by low but distinct fault scarps, providing evidence of very recent tectonic activity. The undulating plains provide foreground and middleground panoramic views with Middleback Range in the south, the hills of Yeltana association (4.4.3) and the Gawler Ranges in the north as background panoramas. The inland salt lakes and intermittent lagoons of Thurlga and Lake Gilles associations (4.4.1, 4.4.4) are important local features and also provide enclosed views. The coastline provides detailed views of tidal flats and mangroves. The region has a mild to warm climate distinguished by low and unreliable rainfall and high summer evaporation. Mean annual rainfall shows little variation over the region, increasing from about 225 mm in the north-east to about 300 mm in the south-west. Temperatures range from mild to warm in summer to cool to cold in winter. Mean monthly evaporation is very high in summer and exceeds the 90th percentile of monthly rainfall for all months of the year. Mean annual evaporation increases from about 2100 mm in the south-east to over 2400 mm in the north.