The NOOLYEANA 1:250 000 sheet area lies in the northern portion of the Great Artesian Basin in South Australia. The area mapped includes the southern part of the Simpson Desert and the very northern end of Lake Eyre North. The oldest outcrops in the area are the Cretaceous (Albian to Cenomanian) claystones and sandstones of the Winton Formation which are exposed in the south-western corner. Ordovician (70 m), Jurassic (149 m) and Cretaceous (1116 m) rocks were intersected in the subsurface in French Petroleum Company (Australia)'s Poonarunna 1 oil exploration well which was drilled in the south-east corner of the sheet area in 1964. Cainozoic rocks include Lower Tertiary fluviatile sandstones which have generally been silicified (together with part of the Winton Formation), Upper Tertiary limestones and marls equivalent to the Etadunna Formation, a sequence of Pleistocene channel sands and clays, aeolian sand of the Simpson Desert and, more recently, the alluvium of the gibber plains, lakes and rivers. Structural trend directions on the map area vary from north-east to north-west.