Seismic refraction and reflection work in the Wallatinna area in 1972 has suggested a fault along the north west edge of the Ammaroodinna inlier as the north west limit of Permian sedimentation, and thus of the Arckaringa basin. This is probably not the limit of the lower Palaeozoic sediments of the Officer basin, which appear to extend south east and perhaps east below the Arckaringa Basin. Refraction velocities over the Wintinna gravity high suggest, but do not positively confirm, the presence of dolomites filling a basement trough. A stratigraphic well, Manya No. 1, has been proposed to identify the refractor at its shallowest point. Target depth is 172 metres. Another shallow well, Marla No. 1, has been proposed to identify the high speed refractor near Wintinna Hill. Refraction velocities in this area are not definitely diagnostic of any known geological horizon, although lower Palaeozoic sandstones of the Officer basin are considered most likely. The predicted depth to the high speed refractor is 102 metres.