Geology

The majority of the shire lies on the Yarragadee formation, formed during the Jurassic period form volcanic and sedimentary rock and consisting of fine to coarse grained sandstone interbedded with shale. The geology underlying the southern coastal boundary between Coorow and Irwin is the Cattamarra Coal Measures. The Cattamarra was formed during the Jurassic period from volcanic and sedimentary rocks and consists of siltstone, shale, claystone, coal and sandstone. The geology underlying the northern coastal boundary between the Irwin and the City of Greater Geraldton is the Kockatea Shale. The Kockatea Shale formed during the Triassic period from volcanic and sedimentary rock and consists of shale, minor siltstone and sandstone.

Deep calcareous sands overlies a series of coastal dune systems and low hills, with relict dunes and limestone outcrops dominating coastal areas. Inland, the landscape is undulating and characterised by deep siliceous sandy soils.

Environment

The shire is located within the Geraldton Hills (GES01) and Lesueur Sandplains (GES02) IBRA sub-regions and is characterised by proteaceous scrub heath and low close acacia shrublands on alluvial plains. The only Threatened Ecological Community known to occur in the shire is the Clay Flats Assemblages of the Irwin River, which is presumed destroyed.  One Priority Ecological Community, Coastal Sands dominated by Summer-scented Wattle Acacia rostellifera, Ooragmandee Eucalyptus oraria and Dongara Mallee E. obtusiflora, occurs in the shire.