The OOLDEA 1:250 000 map area, in the far west of SA, includes portions of the Maralinga Tjarutja Aboriginal Lands, Maralinga Prohibited Area, and Nullarbor Regional Reserve. It is traversed by the Trans-Australian Railway. There is no significant basement outcrop on OOLDEA, and basement interpretation is based on drillhole intersections and aeromagnetic data of varying quality. Basement rocks on eastern OOLDEA belong to the Christie and Nawa Subdomains of the western Gawler Craton. The Christie Subdomain, in the south-eastern map area, comprises Archaean felsic metasediments of the Mulgathing Complex which have been intruded by Palaeoproterozoic to Mesoproterozoic intermediate to felsic rocks of the Ifould Complex. The Nawa Subdomain on OOLDEA consists predominantly of Palaeoproterozoic high-grade metasediments of the Moondrah Gneiss which include magnetite-rich zones of high magnetic intensity. Basement of the Christie Subdomain has been extensively reworked by major northeast-trending mylonitic shear zones. The most prominent of these is the Karari Fault Zone which separates the Christie and Nawa Subdomains. Younger mafic intrusions include dykes related to the Gairdner Dyke Swarm and small plugs within the Karari Fault Zone. The age of the mafic rocks is not known but they may be coeval with Neoproterozoic (Willouran) rift basalts of the Adelaide Geosyncline and Officer Basin. The nature of the basement underlying central and western OOLDEA is unknown and can be interpreted only from low-resolution aeromagnetic data. It is presumably related to the Gawler Craton, and includes zones of high magnetic intensity and two groups of mafic dykes. Basement on OOLDEA, in particular shallow Christie Subdomain basement in the south-eastern corner of the map area, is prospective for gold and other metals. Most of the basement on OOLDEA, except in the south-eastern corner, is overlain by Neoproterozoic sediments of the Officer Basin (Nullarbor Platform). An attempt has been made to correlate the platform sediments with the better known succession in the Marla - Giles area, to the north-east. Probable equivalents of Willouran sediments (Pindyin Sandstone and Alinya Formation) and Marinoan Lake Maurice Group (Tarlina Sandstone, Meramangye Formation and Murnaroo Formation) have been interpreted from drillhole logs, The Officer Basin sediments are prospective for lead-zinc mineralisation (hosted by carbonates) and evaporite minerals (Alinya Formation). Early Cambrian sediments of the Tallaringa Trough (Relief Sandstone, Ouldburra Formation) may extend into north-eastern OOLDEA. The Ouldburra Formation is prospective for evaporite minerals. Minor outcrop of interpreted late Palaeozoic sediments of the Arckaringa Basin occurs near Maralinga, and these sediments may also occur in drillholes in the same area. Equivalents of the Algebuckina Sandstone (Eromanga Basin), with latest Jurassic to Early Cretaceous palynofloras, have been intersected in Maralinga drillholes. Early Cretaceous sediments of the Bight Basin margin (Loongana and Madura Formations) occur in drillholes to the south and west. OOLDEA is located in the north-eastern part of the Cainozoic Eucla Basin. The Eocene-Miocene succession of the Eucla Basin is divided into the Eucla Group of marine platform bioclastic carbonates (Wilson Bluff and Nullarbor Limestones), and the Immarna Group of predominantly terrigenous clastic sediments deposited in shallow marine, coastal and non-marine environments (Pidinga Formation, Hampton Sandstone, Ooldea Sand, Yarle Sandstone and Garford Formation). OOLDEA contains portions of some of Australia's most remarkable landforms. The Nullarbor Plain is the world's largest semi-arid - arid karst region which has developed on the Nullarbor Limestone. Surficial karst features include depressions (dongas) with associated drainage, surrounded by mobile sand and network dunes of the Great Victoria Desert and low rocky rises. In addition, the Nullarbor Plain is interrupted by prominent north to northeast-trending fault scarps, including the Karari Fault scarp, which indicate recent movement of ancient basement structures. The Ooldea and Paling Ranges mark the latest Eocene shoreline of the Eucla Basin. They are interpreted as coastal dunes and appear to be the oldest preserved features of this type in the world. The Ooldea Range extends for ~650 km, from WA to the Ceduna area in SA. Coastal sands of the ranges and adjacent areas (Ooldea Sand, Hampton Sandstone) are prospective for heavy mineral sand deposits. Underlying palaeochannel sediments (Pidinga Formation) have potential for placer gold deposits and other commodities. Quaternary aeolian sand dunes of the Great Victoria Desert cover northern OOLDEA. Their distribution corresponds closely to the distribution of Tertiary coastal sand units from which they have been sourced (Hampton Sandstone, Ooldea Sand, Yarle Sandstone). Tietkens Plain, formed of playa lake carbonates of the Garford Formation, lies in this area.