In June and early July this year, I made two reconnaissance trips to the north of the state to map the western limits of portion of the Great Artesian Basin Sediments. The western extent of the Bulldog Shale (Freytag 1966) and the Coorikiana Sandstone (op cit) was investigated as a contribution to the state geological map (on a scale of 1:1 000 000). Its detailed mapping was undertaken. Areas covered included the Abminga, Billa Kalina, Cooper Pedy, Curdimurka, Lake Eyre, Murloocoppie, Warrina and Wintinna 1:250 000 sheets area (see locality map). Dr H Wopfner was able to give some idea of the positions of these boundaries which helped immensely the planning of the trips and saved considerable time (see Handbook of the Geology of South Australia p 151). Folded mosaics and photographs were used for navigation and location with notes either in a field book or on the backs of photographs. A map has been prepared showing the two boundaries from the Northern Territory border to just east of Marree. Bore logs and seismic shot hole logs were used to plot the lower boundary of the Bulldog Shale.