An aeromagnetic reconnaissance to indicate the eastern margin of sedimentary rocks in the Rawlinson Range-Young Range area of Western Australia was flown in October 1960. The reconnaissance consisted of two groups of traverses west of Giles. Each group consisted of three traverses in a triangular pattern. Aeromagnetic traverses were also flown from Alice Springs to Giles and from Giles to Kalgoorlie; data from these traverses and from others flown in previous years were used to evaluate the results of the reconnaissance. The results indicate that the boundary of the region where the magnetic basement is either very shallow or crops out follows a line from the eastern part of the Rawlinson Range, west and south-west to Mt. Charles, then south-east and south to Axe Hill. The boundary then turns east towards Skirmish Hill before it swings south-east along the northern edge of the Officer Basin. Sedimentation west of this boundary could reach depths of more than 10,000 ft over a considerable area but much of the sedimentary rocks could be of Proterozoic age. The western boundary of the sediments was not determined.