Eyre and Yorke Peninsulas (Province 4)
The steeply rising Mt Lofty Ranges clearly define the eastern limit of the Eyre and Yorke Peninsulas Province. On Eyre Peninsula the province extends north to the Gawler Ranges and north-west to the margin of the Great Victoria Desert dunefields, where the limit of wheat cultivation provides a cultural boundary.
The climate of this province is relatively mild and moist in the coastal south and south-west, and warmer and drier in the north and north-east. On Eyre Peninsula, mean annual rainfall is about 500 mm in the extreme south, decreasing to about 225 mm in the north-east. Slightly higher elevation in the vicinity of Cleve and Kimba is associated with a mean annual rainfall of over 400 mm. On Yorke Peninsula, mean annual rainfall decreases from around 450 mm in the extreme south to less than 350 mm in the north near Port Pirie. Monthly rainfall generally indicated a winter maximum which is less distinct in the north where it is low throughout the year.
Temperatures are generally mild to warm and there is a gradual decrease in seasonal and diurnal ranges towards the north and inland. Throughout the province mean monthly evaporation generally exceeds median monthly rainfall for every month of the year.
The more important landforms of the Eyre Peninsula are the uplands along the east coast and the undulating calcarenite and calcrete plains and dune fields on the centre. Yorke Peninsula and the country tot he east comprise gently undulating calcrete plains mostly without dunes. Where they do occur, they are less frequent than on Eyre Peninsula.
Three broad types of native vegetation occur in the province reflecting the increasing aridity of eth climate from the south to the north-east. There are low open forest and woodland; mallee; and low open woodland with a bluebush understory. On both peninsulas there has been extensive clearing for cultivation and grazing, but Eyre Peninsula still has large tracts of mallee.Rural land use in the province is dominated by a rotation of cereal cultivation and livestock grazing, which is more intensive on Yorke Peninsula than on Eyre but there are small areas used exclusively for grazing in the north and west of Eyre Peninsula. The major cereals are wheat and barley and their sowings represent around 75% and 70% respectively, of the State's total area. Sheep are by far the most important farm animals; on Yorke Peninsula they are mainly grown for meat production; on Eyre for wool.
The main factors limiting land use in the province apart from climatic are wind erosion and salinity. Wind erosion is common on lighter textured soils; the whitish calcareous sands of the coastal dunes suffer the most sever erosion, followed by the brown and red sands of the inland dunes. The shallow loams and calcareous earths of the calcarenite plains are affected by slight to moderate drift. Salt accumulation commonly occurs in low-lying areas, especially where there is only local drainage.
Six environmental regions are recognized in this province:
Southern Highlands and Plains (Environmental Region 4.1)
This region includes the southern part of the uplands on the east coast of Eyre Peninsula, and the plains to the south and west.
West Coast (Environmental Region 4.2)
This region is the undulating to hilly dune-free calcarenite plain with low rises and occasional steep-sided quartzite and conglomerate ridges on the west coast of Eyre Peninsula. Its shallow sandy soils have a low water-holding capacity which is reflected in the arid appearances of this region.
Central Mallee Plains and Dunes (Environmental Region 4.3)
This region extends across Eyre Peninsula from its western extremity to Spencer Gulf. It is distinguished climatically by being more arid than the regions to the south. It is essentially an undulating plain with an extensive cover of dunes and sandsheets.
Northern Myall Plains (Environmental Region 4.4)
This region lies north-east of Region 4.3 and is geomorphologically similar to it but has been separated because of a distinct difference in vegetation from mallee scrub to myall woodland and a change in land use from rotation wheat cultivation to extensive livestock grazing. The area mainly comprises undulating plains with calcrete development. Dunes and sand sheets occur locally, as do salt lakes and flats.
Southern Yorke Peninsula (Environmental Region 4.5)
This region comprises the lower section of Yorke Peninsula; its landforms resemble those of central Eyre Peninsula, except that dunes are less common.
Gulf Plains (Environmental Region 4.6)
This region includes the northern section of Yorke Peninsula and the plains and fans between Gulf St Vincent and the Mt Lofty Ranges. Most of the region consists of undulating plains with calcrete duricrusts but without dunes. Near the Mt Lofty Ranges the plains have a definite slope gradient and merge eastwards with the alluvial fans from the ranges.
