This report presents the results of a study by the Geological Survey of South Australia (GSSA) and CSIRO Mineral Resources to estimate depth to basement over the COOMPANA area of south-western South Australia. The study uses magnetic field data acquired on a 2014–2015 airborne magnetic and radiometric survey that was commissioned by the GSSA as part of the PACE Initiative. It is important when using magnetic source depth estimates to understand their limitations. The inverse problem of determining source characteristics from measured magnetic field variations is fundamentally non-unique, and solutions can always be found at any shallower depth for magnetisation distributions which are more diffuse. Despite these limitations, magnetic depth estimation is a valuable and generally reliable method of estimating depths to geological features. This is because many instances of geology provide compact magnetisations with abrupt, steep-dipping contacts, well matching the source model assumptions. Magnetic source depths are the primary product of this depth estimation study. These are assumed to map the top of magnetisations terminated at the basement unconformity surface, and thereby to provide spot samples of that surface. The solutions can be used in their own right, or may be incorporated into any 3D geological models of the area. We have also generated a proposed basement depth surface from the solutions, assuming that the points sample a single surface, and that the surface varies smoothly between solutions. We used contouring constrained with textural variations in the vertical derivative enhancement of the total magnetic intensity (TMI) grid to guide our interpretive interpolation of the surface. This surface is necessarily more speculative than the point solution values on which it is based. The estimated magnetic source depths, models and interpreted surface are all available in a digital package released with this report.