The Glen Mountains layered complex (GMLC) of the Wichita Mountains of Oklahoma is a coarse-grained analog to Layer 3 gabbros of the sea floor. The slowly cooled, mafic, layered complex developed in the site of an aulacogen, which is interpreted as a failed, intracontinental rift. The remanent magnetism of rocks of the layered complex is extremely stable due to the presence of magnetic inclusions in the major phases, primarily plagioclase. The early formation of plagioclase facilitated the formation of these magnetically important inclusions. Petrologic processes that promote the formation of magnetically stable mineralogic inclusions in coarsegrained gabbros should be operative in oceanic slow-spreading ridges. Therefore, the contribution of magnetization of Layer 3 gabbros should be greater in slower spreading ridges than in faster spreading ridges because of their differences in petrologic evolution.