A regional magnetic map for southwestern Manitoba and southeastern Saskatchewan (areas not covered by the Federal–Provincial aeromagnetic maps) has been compiled. After a review of the geological and geophysical characteristics of the Superior–Churchill boundary zone in northern Manitoba, the new compilation magnetic map was used as a guide for tracing the boundary zone southwards to the Canada–U.S.A. border.By comparing the patterns on the new magnetic map with those on the neighbouring Federal–Provincial aeromagnetic maps, the major east–west trending crustal belts in the Superior Province have been extended farther west than was previously possible. In addition, a major granite/greenstone terrain, which extends in a southerly direction from a region near Flin Flon to the Canada–U.S.A. border, has been delineated in the Churchill Province. To the west of this granite/greenstone terrain, in central Saskatchewan, there is an extensive region of low magnetic relief, similar to that observed across the Kisseynew gneiss belt in northern Manitoba.