Geology

The western portion of the shire is located on the Yarragadee formation which consists of fine to coarse grained sandstone interbedded with shale and was formed during the Jurassic period from sedimentary and volcanic rock. The eastern scarp of the Yarragadee is dominated by the Otorowiri formation, which was formed during the Cretaceous period from sedimentary and volcanic rock interbedded with siltstone, shale and sandstone. The Parmelia group lies east of the Otorowiri formation, was formed during the Mesozoic era from sedimentary and volcanic rock and consists of sandstone and siliciclastic sediments. Underlying geology east of the Parmelia group is the Yandanooka Group, formed during the Neoproterozoic era from sedimentary and volcanic rocks and consisting of siltstone with abundant volcanic fragments and sandstone. The Nangetty formation underlies the town site of Three Springs and was formed during the carboniferous- permian period from sedimentary and volcanic rocks. The Nangetty formation consists of diamicitite, shale and sandstone.

The eastern portion of the shire is dominated by the Coomberdale subgroup. The Coomberdale subgroup comprises of sandstone, siltstone, dolomite rock and silica minerals. The Billeranga subgroup forms the western scarp of the Coomberdale subgroup and was formed during the mesoproterozoic era from volcanic and sedimentary rock. The Billeranga subgroup consists of sandstone, siltstone, basalt and volcanic sand. Lying east the Coomberdale subgroup is Gneiss which forms a part of the south west terrain of the Yilgarn Craton.

The landscape is undulating with low hills and dunes. Soils are predominately deep siliceous sands. Calcareous loamy soils overlies hill slopes formed below breakaways. The soils underlying the eastern portion of the shire are calcareous loamy soils and deep siliceous sandy soils associated with low hills and rocky outcrops. The eastern portion of the shire is characterised by saline lake systems and alluvial plains.

Environment

The shire is located within the Lesueur Sandplains (GES2) and Merredin Ancient Drainage Basin (AVW01) IBRA sub-regions and is characterised by proteaceous heath. The endangered plant assemblages of the organic mound springs of the Three Springs area are endemic to the shire. This habitat is recognised as Threatened Ecological Community (TEC) protected in Western Australia. The mound springs are characterised by continuous discharge of groundwater into raised peat wetlands and provide stable, permanently moist microhabitats supporting diverse plants and invertebrates. Moisture loving plants found in the mound springs include moonah Melaleuca preissiana, river gum Eucaluptus camaldulensis, endangered white myrtle Hypocalymma angustifolium, sheath twigrush Baumea vaginalis and other sedges. Patches of the vulnerable Ferricrete Floristic Community and Plant Assemblages of the Inering System TECs are also found in the shire.