In an area of limited outcrop on the western margin of the Gawler Craton, gravity and aeromagnetic interpretation is used to delineate basement units. Fault structures divide the Nullarbor and Fowler 1:250 000 sheet areas into five zones. The western zone is an area of deep basement (2000m). Prominent in this zone is a large circular, intrusive body 5000m deep and 10,000m radius at the intersection of two major faults. Three central zones constitute the margin of the Gawler Craton. They contain linear magnetic anomalies and the interpreted rock types are basic with some banded iron formations. These zones are indicative of high grade metamorphic rocks and interpreted depths range from 1000m to less than 500m. The eastern zone (on Fowler) is within the central area of the Gawler Craton and contains acid rock types. Several large granitic bodies are outlined and depths in this zone are shallow with occasional basement outcrops.