Five calc-alkalic plutonic belts, developed mostly during Mesozoic time, are definable in southern Alaska. These belts may represent parts of magmatic arcs developed during episodes of subduction, and at least four appear to be temporally and spatially distinct. Age relations indicate that 10- to 30-m.y. intervals are sufficient for the generation and emplacement of the individual plutonic belts. Any overlapping sequence of tectonism, volcanism, and sedimentation that may have accompanied regional plutonism apparently ended within an interval of 20 to 55 m.y. The space-time relations of Mesozoic plutonism in southern Alaska suggest that more flexible evolutionary models and greater temporal resolution are needed to reconstruct the tectonic history of the region.