The presence of only three major tectonostratigraphic terranes (TSTs) in southeastern Alaska and northwestern British Columbia (Chugach, Wrangell, and Alexander) is indicated by critical analysis of available age, stratigraphic, and structural data. A possible fourth TST (Stikine) is probably an equivalent of part or all of the Alexander. The Yakutat "block" belongs to the Chugach TST, and both are closely linked to the Wrangell and Alexander(-Stikine) TSTs; the Gravina "TST" is an overlap assemblage. The Alexander(-Stikine) TST is subdivided on the basis of age and facies. The "subterranes" within it share common substrates and represent large-scale facies changes in a long-lived island-arc environment.

The "Taku TST" is the metamorphic equivalent of the upper part (Permian and Upper Triassic) of the Alexander(-Stikine) TST with some fossil evidence preserved that indicates the age of protoliths. Similarly, the "Tracy Arm TST" is the metamorphic equivalent of (1) the lower (Ordovician to Carboniferous) Alexander TST without any such fossil evidence and (2) the upper (Permian to Triassic) Alexander(-Stikine) with some newly discovered fossil evidence.

Evidence for the ages of juxtaposition of the TSTs is limited. The Chugach TST deformed against the Wrangell and Alexander TSTs in Late Cretaceous. Gravina rocks were deformed at that time and also earlier. The Wrangell TST was stitched to the Alexander(-Stikine) by middle Cretaceous plutons but may have arrived before its Late Jurassic plutons were emplaced. The Alexander(-Stikine) and Cache Creek TSTs were juxtaposed before Late Triassic.

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