Declared Rare and Poorly Known Flora in the Geraldton District

The large pastoral proportion of the District is reflected in the fact that most of the Declared Rare Flora are found on itswestern side, with few on the eastern side, which is also less well known and less surveyed botanically. The proportionof Declared Rare Flora populations in the District which occur on road and rail reserves is less (a quarter of the totalnumber of populations, compared to a half in the Moora District), than in other Districts further south, which alsoreflects the difference in land use between this District and those which are mainly within the South-West BotanicalProvince. Even in the north-west of the District most of the Declared Rare Flora populations occur on pastoral leases,the national park or other Crown land.The impact of fungal disease in the District is low. Most of the area has rainfall levels which are too low to supportinfections of Phytophthora species. The south-west corner of the District, where rainfall levels are higher, has largeareas of sandplain over limestone, which are well drained and therefore unlikely to provide suitable conditions for thespread of dieback. An area in the north-west of the District reported to have an infection of a species of Phytophthorain the mid 1980s has been monitored since but the disease has not been reconfirmed there.6.1 ClimateThe climate of the Geraldton District varies considerably from the coastal belt inland to the eastern limit of the District.Rainfall decreases from an annual average of ca. 500 mm in the south-west of the District near the coast to ca. 200 mmin the north-east in the dry inland areas. Near the coast in the Geraldton area the climate is defined as dry warmMediterranean, with cool, wet winters and hot, dry summers, the rainfall sufficient for four winter months for crops tobe grown, whilst the remaining eight months of the year are generally dry. Further inland in the Yalgoo area, the semidesertclimate still has a winter maximum rainfall and is also Mediterranean, with fairly reliable winter rain and someadditional summer rain from thunderstorms. Further inland, for example, as at Cue, the climate is desert, with bothwinter and summer rainfall peaks. Here the summer rain is received from tropical cyclones moving in a southerly orsouth-easterly direction. Winter rainfall from southern depressions is dependable only along the coastal belt as only thestrongest depressions penetrate far enough inland to bring any effective winter rain, and in this inland area neithersummer or winter rainfall is reliable and in some years, no rain falls.Temperatures in the District vary from a mean February maximum of 32.2° C and a mean July maximum of 19.4° C atGeraldton, to a mean January maximum of 37.7° C and a mean July maximum of 18.4° C at Yalgoo, and at Cue, a meanJanuary maximum of 37.8° C and a mean July maximum of 18.2° C. Mean minimum temperatures range from 8.8° Cin September at Geraldton to 6.1° C in July at Yalgoo and 6.9° C in July at Cue.6.2 Geology, Landforms and SoilsMuch of the eastern part of the District is part of the Archaean Yilgarn Block, which is composed mainly of gneissesand granites, with minor infolded belts of metamorphic sedimentary and igneous rocks. The metamorphic rocks consistof a wide variety of volcanic and sedimentary assemblages, including basalts, lavas and tuffs, banded ironstone,jaspalite and chert, and shale, siltstone, sandstone, greywacke and conglomerate. The mafic (basalt) rocks are known asgreenstones and the sediments as whitestones. The rocks of the metamorphic belts are harder and more resistant thangneiss and granite, so they form ranges of hills, the granites and gneiss underlying sandplains and other plain areas. Themetamorphic rocks are also of economic importance as a result of their mineralisation, and are mined for gold, nickel,copper and iron ore.The western boundary of the Yilgarn Block is mainly formed by the Darling Fault which runs northwards through theDistrict from east of Arrino in the south, to just west of Mullewa and north to the Greenough River near BarraweelbarraHill and thence to the northern boundary of the District just east of the Murchison River at Mulla Mulla Flat. In theDistrict, it does not form a feature visible on the ground as it does nearer Perth.West of the Fault, the edge of the continent has subsided into the Perth Basin, which was submerged and became filledwith sediments. Since the end of the Cretaceous period, the area has been above sea level and has become weatheredand denuded. Part of the Geraldton area did not become submerged with the Perth Basin. This is the NorthamptonBlock, which formed an island of Proterozoic rocks until Mesozoic time when it was covered with a thin sequence offlat Jurassic and Cretaceous rocks. The rocks of this Block have been metamorphosed and are mainly of granulites andquartzites, with large intrusions of granite. The rocks deposited in the Perth Basin are sandstones and shales. Some ofthe Permian rock contains coal seams and the youngest Cretaceous rocks consist of radiolarite and chert.A second fault, the Urella Fault, runs parallel to the Darling Fault and lies about 20 km west of the latter in the Dongaraarea. The Irwin Sub-basin lies between the two faults and has a narrow belt of Precambrian metamorphic rocks to the17