The YARDEA 1:250,000 scale regional geological map area straddles the southern margin of the Gawler Ranges on northern Eyre Peninsula. The only major township within the area is Minnipa, with Kimba and Wudinna both located immediately south of the map boundary, and the smaller community centre of Buckleboo in the south-eastern comer of the map. The Eyre Highway crosses the south-western corner of the map, which is bound by latitudes 32°00'S and 33°00'S, and longitudes 135°00'E and 136°30'E. The Archaean to Mesoproterozoic basement rocks present on YARDEA form part of the eastern Gawler Craton. They represent the northern exposures of the Cleve and Coulta Subdomains of the Gawler Craton, and the eastern margin of the Nuyts Subdomain. The Cleve and Coulta Subdomains consist of Archaean to Palaeoproterozoic metasediments, metavolcanics and plutonic rocks deformed into a north to northeast-trending foldbelt extending from southern Eyre Peninsula to the Gawler Ranges, where they are concealed by Mesoproterozoic Gawler Range Volcanics (GRV) and associated intrusives (Hiltaba Suite) and sediments. The Nuyts Subdomain consists mainly of late Palaeoproterozoic felsic granitoids with local felsic volcanics and mafic dykes. It too is overlain by GRV and intruded by Mesoproterozoic intrusives. Relatively thin Cainozoic sediments cover portions of the Precambrian basement, particularly south of the Gawler Ranges where the superficial cover is widespread. Regional and detailed geological investigations elsewhere on Eyre Peninsula have recognised the complex structure and stratigraphy of the Archaean to Palaeoproterozoic sequence, especially for the Middleback Range, for central and southern Eyre Peninsula, and for north-eastern Eyre Peninsula. The garnetiferous Archaean Carnot Gneisses (paragneisses) of the Coulta Subdomain of southern Eyre Peninsula have been recognised as extending north into the Kyancutta - Warramboo area immediately south of YARDEA, where they contain local iron-rich interbands inferred to represent original banded iron formation. The Cleve Subdomain extends into the south-eastern quadrant of YARDEA, and is comprised mainly of tightly folded and metamorphosed metasediments of the Palaeoproterozoic Hutchison Group. The deformation and metamorphism of these metasediments occurred during the Kimban Orogeny, and was accompanied by the syntectonic intrusion of granites and the formation of major mylonitic shear zones, which extend north to northwestwards onto YARDEA from the KIMBA and WHYALLA map areas. Based on very limited Rb-Sr or U-Pb zircon geochronology that has been undertaken on the Archaean to Palaeoproterozoic rocks, four broad subdivisions of granitic orthogneiss have been regionally identified : Sleaford Complex (~2600- 2400 Ma), syn-Kimban Orogeny Lincoln Complex (~1850-1710 Ma), Ifould Complex (~1685-1670 Ma) and St Peter Suite (1635-1610 Ma). However, these subdivisions can be further refined based on geographic distribution, composition, structure and geochemistry. The older Lincoln Complex granitoids (~1850- 1840 Ma Donington Suite) appear to be restricted to east of the Kalinjala Mylonite Zone, while the younger Lincoln Complex granitoids (~1780-1710 Ma) are widespread throughout the Cleve Subdomain west of that shear zone. The Ifould Complex has been defined as comprising only those granites formed at ~1685-1670 Ma (e.g. the Symons and Carappee Granites). Observations on the Mesoproterozoic geology of the Gawler Ranges date back to those of H.Y.L. Brown in 1885. Regional aerial photo interpretation by A.R. Crawford in 1963 disclosed a number of semi-circular structures in the Gawler Ranges that were interpreted as relict evidence of volcanic centres. The first geochronological study done on the GRV and Hiltaba Suite granites was by Compston et al. in 1966, which established their Mesoproterozoic age. Starting in 1972, A.H. Blissett of the South Australian Department of Mines and Energy undertook a 15-year regional mapping program of the entire Gawler Ranges Volcano-Plutonic Province, including the YARDEA 1:250,000 map area, which map was then published in 1988. Complementary stratigraphic, petrological, geochemical, geochronological and evolutionary theoretical studies on the GRV rocks were subsequently carried out by many specialist workers. A major late Proterozoic bolide-impact structure has recently been interpreted, centred on the Lake Acraman salina, which was originally considered to be a probable volcanic centre.