The area embraced by the Andamooka and Torrens 4-mile geological sheets is defined by long 136° 30- long 138° 00 and lat 30° 00- lat 32° 00 and comprises an extensive partially dissected plateau west of Lake Torrens, the Lake Torrens sunkland and part of the Willouran Range. The 24 one-mile map sheets included in this area are indicated in figure 1. It is an area of low rainfall being in the 4¾ to eight inches per annum range, and constitutes part of the northwest pastoral district of South Australia. To the north of the vermin fence which transects the Andamooka sheet, on Stuart Creek and Billa Kalina pastoral stations, cattle are raised while to the south the area includes all or part of the following stations which are devoted to sheep and wool production: Witchelina, Mulgaria, Andamooka, Roxby Downs, Parakylia, Purple Downs, Arcoona, Bosworth, South Gap, Pernatty, Oakden Hills, Yalymboo, Mahanewo, Yudnapinna, Yadlamalka, Myrtle Springs and Wirraminna. Stock are dependant on indigenous perennial plants – the staple fodder comprising salt bush and blue bush with a carrying capacity of less than 25 sheep per square mile. There are only two townships in the area – Woomera with a population of 5000 and Andamooka with a ‘floating’ population and in November, 1964 numbering 1000 persons, including 150 aboriginals. The Transcontinental Commonwealth Railways line (4ft 8½ inches) connecting Port Pirie and Kalgoorlie passes through the area, with fettlers and control staff located at a number of sidings along the route. The main road connection between Port Augusta and Alice Springs, the Stuart Highway, more or less parallels the railway line in this region. It is a graded dirt and gravel road whose general condition varies greatly from time to time depending on seasonal conditions, usage and degree of maintenance. The section of the main road between Wirrappa R.S. and Woomera village and certain installation access roads within the “restricted area” have been sealed. The road connection northwards to the opal field at Andamooka is generally kept in good repair as a re the tracks that serve as access routes to the various station homesteads. Elsewhere the tracks are in varying states of repair depending on the terrain, usage and degree of local maintenance. Mineral output has been sporadic, and, apart from the production of opal, of no great importance. Great strategic importance has been conferred on this region by the joint decision of the British and Australian Governments to establish on the fringe of the desert, within reasonable distance of laboratories, research and assembly facilities at Salisbury, a land range for the testing, firing and recover of long range weapons and guided missiles. Woomera village, located in the central western part of the area and located in a “prohibited area” in which access and movement are restricted, was created as a township to serve the range. The generally desolate, flat terrain, free of natural barriers has provided an ideal site. Regional geological mapping of the area was initiated in 1959 and was completed in 1964; field work occupied 30 man weeks. The writer was assisted at various times during the course of the work in the field by M.N. Hiern, L.G. Nixon, B.G. Forbes and J.G. Olliver. All tracks in the area were traversed and detailed mapping confined to critical localities and to areas where this was considered desirable. Geological boundaries were thus delineated, spoil from all wells and dams was examined and attention was given to mineral occurrence, particularly to the copper and manganese deposits of the Pernatty Lagoon – Mount Gunson district and to opal at Andamooka. Further subdivisions of the Adelaide System in the region were made following formal definition of these units in the Copley region by R.P. Coats, and the writer benefitted greatly from co-ordination with him in map preparation. The following report accounts the geological investigations and includes notes on physiography, climate, vegetation, hydrology and mineral resources of the region.