The LAKE EYRE 1:250 000 sheet area is located about 750 km north of Adelaide on the south-western margin of the Great Artesian Basin. The map area incorporates 15 950 square km, with Lake Eyre itself covering about half of this area. The oldest exposed rock unit is the early Cretaceous Bulldog Shale. Younger sediments include the early to middle Cretaceous Oodnadatta and Winton Formations (870 m), the Tertiary Eyre and Etadunna Formations (90 m) and a sequence of Quaternary deposits. In 1964, French Petroleum Company (Australia) drilled an oil exploration/stratigraphic well, Poonarunna 1, a few kilometres north of the north-eastern corner of the sheet area. The well intersected Tertiary (of 90 m thickness), Cretaceous (1116 m) and Jurassic rocks (420 m), and bottomed in steeply dipping ?Ordovician siltstones (>69 m). No hydrocarbon occurrences were encountered. The Mesozoic sediments in Poonarunna 1, which unconformably overlie the Lower Palaeozoic rocks, dip gently towards the north-east. Their structural trends are in a dominant north or north-westwards direction, consistent with those observed in surrounding portions of the Great Artesian Basin. No economic mineral deposits have yet been discovered within the map area.