A field mapping project was set up by PIRSA to investigate the age, origin and emplacement history of newly discovered [by Goldstream Mining NL on EL 2222] volcanic rocks within the Mount Grainger Anticline, close to the town of Oodla Wirra. Outcrop of these Oodla Wirra Volcanics (OWV) was found to be more common than previously mapped. The OWV were seen to encompass a variety of volcanic facies, including felsic coherent, pyroclastic and volcaniclastic deposits. The majority of outcropping volcanic rocks are silica-altered, with silica replacing most of the original mineralogy, resulting in the remaining lithology being defined by quartz eyes and reddish oxidised areas that have arisen through weathering. The OWV are believed to have been deposited within evaporitic siltstones of the Callanna Group. A U-Pb Shrimp II date of 802 ± 12 Ma (pooled age) was obtained from felsic tuffaceous rocks. This age is comparable to that of the Rook Tuff (at 802 ± 10 Ma), another volcanic unit which also occurs within the Curdimurka Subgroup of the Callanna Group. The inconsistent strike of the volcanics and surrounding Adelaidean stratigraphy, plus the incoherent nature of the outcrop, presence of newly mapped breccia, and the observed proximity of Callanna Group sediments and OWV to much younger strata, has led to the interpretation of a large disturbed zone in the mapped area, which is attributed to a history of diapir formation. The area now inferred as being diapiric has therefore extended the main body of the Mount Grainger diapir 6 km to the south. Large rafts of intact Adelaidean strata are surrounded by diapiric breccia carrying clasts of OWV, mafics and Callanna Group sediments. The Oodla Wirra Fault has apparently played a major role in the location and formation of the diapir.