The Yass 1:100000 sheet covers an area of about 2600 square km, and is located about 320 Km southwest of Sydney in the fertile grazing country of the southwestern slopes of New South Wales. Steeply dipping slates of Ordovician age (Jerrawa Beds) are the oldest rocks found in the area. Theses rocks are overlain, with apparent unconformity, by the Mundoonen Sandstone of Silurian age. The Douro Group, a thick sequence consisting dominantly of tuffs and volcanics, overlies this formation and covers about 60 per cent of the map area. The almost complete absence of bedding in these rocks makes the study of their geological structure very difficult. The overlying Laidlaw and Silverdale Formations and Booroo Ponds and Barambogie Groups consist of a fossiliferous sequence of sediments, with shales and limestones dominant. This sequence is limited in areal extent to the Yass Basin. The Black Range Group, a dominantly volcanic sequence, is of Early Devonian age. Mapping of the Kirawin Shale within this sequence in the Burrinjuck Dam area has outlined a number of fold structures. The Murrumbidgee Group overlies the Black Range Group and consists dominantly of complexly folded fossiliferous limestones. Granitic rocks intrude the Silurian sequence, but their outcrop occupies only a relatively small proportion of this sheet. The Geological Survey of New South Wales 1:100000 mapping programme covers areas of special geological or mineral resource interest within New South Wales. The Yass sheet contains the Yass and Taemas area, which have come to be regarded as classic for the study of Silurian and Devonian sedimentation on the stare. A considerable amount of stratigraphic and paleontological information has been published on these areas and they have been visited by students of geology for many years.
Cramsie, J.N., Pogson, D.J., and Baker, C.J., 1978. Geology of the Yass 1:100000 Sheet 8628. New South Wales Geological Survey, Sydney.