A common problem in interpreting aeromagnetic data involves mapping of a single magnetic crystalline basement interface overlain by nonmagnetic sedimentary rocks. The solution of this problem, as discussed in Pilkington and Crossley (1986), provides important geologic information. However, difficulties arise where the magnetic effects of the crystalline magnetic interface are obscured by intrusives or volcanic flows within the sedimentary sequence. The resulting problem in the interpretation requires separation of the two effects, so that the modeling problem will be tractable. Unfortunately, in view of the spectral overlap of fields from sources at different depths (e.g., Bhattacharyya, 1966), a perfect separation is not possible. This condition has led to the subjective approach of simply dividing the observed field into low-wavelength and high-wavelength parts and interpreting each one independently (Lehmann, 1970; Sprenke and Kanasewich, 1982). An alternative method has been advocated by Spector and Parker (1979) who separate the two effects based on power spectral analysis of the observed field.