This progress report summarises the field characteristics of the major rock types of the BIRKSGATE 1:250 000 mapsheet area. The crystalline basement rocks are granite gneisses and granites of the Musgrave Block. These are of uncertain age and are referred to as Older Precambrian. These rocks are overlain unconformably by the basal conglomerate of a sandstone sequence of Adelaidean age. There was apparently continuous deposition of micaceous sandstones and arkoses from the Marinoan into the Cambrian. All these sediments were folded gently, probably during the Upper Cambrian. This mild tectonic event was followed by a sill-like intrusion or flow of a tholeiite which was in turn succeeded by a sandstone and siltstone sequence. The K-Ar age of the tholeiite is a minimum of 480 million years (i.e. Lower Ordovician), but the age of the overlying sediments is not known with any certainty. Silcrete was developed close to a land surface during the Tertiary. Chalcedonic limestone was later deposited in shallow fresh-water lakes during the Late Tertiary or the Early Quaternary. A superficial deposit of sand dunes from a Quaternary arid period covers much of the sheet area.