The crystalline basement of COOBER PEDY comprises portion of the northern part of the Gawler Craton. Outcrop is scattered and is generally intensely weathered. Sediments, including sandstone, arkose and banded iron formation, were deposited on an Archaean basement during the Late Archaean to Early Proterozoic. Metamorphism that reached granulite facies grade occurred at about 2400 Ma, accompanied and followed by the formation of syn- to post-orogenic granites equivalent to the Glenloth Granite. Collectively these metasediments and foliated granites form the Mulgathing Complex, which is considered to constitute much of the basement of the southern half of COOBER PEDY. Similar metasediments and gneisses, associated with banded iron formations at Mount Christie on TARCOOLA and at the Mount Woods Inlier on BILLAKALINA, give contrasting ages of 2400 Ma and 1500 Ma respectively. This poses a problem to be resolved. A second metamorphic event, reaching upper amphibolite facies and showing evidence of retrogression, represents the Middle Proterozoic Kimban Orogeny of south-eastern Eyre Peninsula. The intrusion of the Gawler Range Volcanics around 1500 Ma marked the consolidation of the Gawler Craton. Eight basement provinces have been interpreted. Their overall trend is north-east to east, similar to that determined as being the overall trend of observed layer parallel foliations. A prominent fault belt comprising the Karari, Wallira and Faulkness faults may separate basement which was strongly deformed and metamorphosed during the Kimban Orogeny near the centre of the map area (Province 3) from less affected rocks of the Mulgathing Complex to the south (Province 2). A fault-bounded north-easterly continuation of the Tallaringa Trough from TALLARINGA onto COOBER PEDY is interpreted, having a seismically interpreted maximum depth of about 400 m. The most northerly known outcrop of Gawler Range Volcanics (Province 7) in South Australia occurs in the vicinity of Perfection Well on the north-eastern margin of the Gawler Block. Following cratonization, epeirogenic movement along prominent north-east, north-west and east-northeast aligned lineaments resulted in the formation of the Adelaidean-Palaeozoic Officer Basin and the Permian Arckaringa Basin.