The MARREE mapsheet area includes the south-western portion of the Strzelecki Desert plus parts of the Tirari Desert, north-western Flinders Ranges and north-eastern Willouran Ranges, between latitudes 29 to 30 degrees S and longitudes 138 to 139 degrees 30 minutes E. This ~15 000 square km area is predominantly arid, with hot dry summers and cool winters: sporadic rainfall may occur from autumn to late spring, when heavy downpours can cause flash flooding that impedes surface travel. Within the area lie parts of three large drainage sinks or playas forming the ephemeral Lakes Blanche, Eyre North and Gregory. Numerous creeks debouch from the highlands and drain towards these playas, either towards Lake Eyre to the west or north-westwards onto the CURDIMURKA and LAKE EYRE mapsheet areas. Relief on MARREE is broadly flat to convex, and the topography is partly covered by desert dunefields. The high ground of the ranges comprises folded Neoproterozoic sedimentary rocks of the Adelaide Geosyncline, underlain in the Flinders region by much older dense crystalline rocks composed of highly deformed Mesoproterozoic metasediment rafts and keels supported by variably deformed Mesoproterozoic granites and volcanics. The surrounding plains are underlain by sediments of the Cambrian Arrowie Basin, Cambro-Ordovician Warburton Basin and Permian Cooper Basin, and have exposures of Devonian marine sediments and basaltic volcanics plus Mesozoic Eromanga Basin and Cenozoic Lake Eyre Basin sediments. Erosion and deposition continue to be active in many areas today. Crustal deformation occurred during the early Mesoproterozoic (~1580 to 1560 Ma), then basic dykes were injected during a long period of tensional stress (~1100 to 500 m. Warping of strata deposited in the Eromanga and Lake Eyre Basins has formed a series of regional dome structures, one of which is the Cooryanna Dome, the southern portion of which occupies about 15% of MARREE. Field mapping and compilation done in the mapsheet area as a whole recognises a total of 140 rock units. Fossils found on MARREE include poorly preserved Neoproterozoic stromatolites and trace fossils from the Cambrian. Shelly fauna, trace fossils, carbonaceous flora and coal have been recovered from the Eromanga Basin succession. The Cretaceous Neales River Group commonly contains abundant shells, calcified wood and many animal burrows. Leaf impressions, animal burrows, and vertebrate bones and teeth occur within the lower to middle Cenozoic units, but are not common. Quaternary units have yielded some vertebrate bones from the once common Australian Megafauna. These finds include fossil remnants of Diprotodon sp., large wombats and kangaroos. Mineral prospecting and exploration undertaken on MARREE since the 1870s have located Pb, Zn, Ag, Cu, Fe and associated Sb, As, Sn, Co, Cd, Bi, V, and trace Au mineralisation. Rare earth elements (including U) are also known from this area. Non-metallic minerals present include talc, dolomite and magnesite. Mining has extracted Zn, Pb, Ag, Cu, minor Sb, As, small amounts of Au, and abundant talc. Groundwater is a valuable commodity and is widely used by MARREE area residents, regional pastoralists, stock and wildlife. A significant amount is drawn from the Eromanga and Lake Eyre Basin aquifers. Artesian groundwater from the Eromanga Basin flows to the surface via mound springs (natural desert oases) and bores. Many bores were drilled between the 1880s and 1990s.