We investigate the crustal structure and tectonic evolutionof the North American continent in Alaska, where the continenthas grown through magmatism, accretion, and tectonic under-plating.In the 1980s and early 1990s, we conducted a geological andgeophysical investigation, known as the Trans-Alaska CrustalTransect (TACT), along a 1350-km-long corridor from the AleutianTrench to the Arctic coast. The most distinctive crustal structuresand the deepest Moho along the transect are located near thePacific and Arctic margins. Near the Pacific margin, we infera stack of tectonically underplated oceanic layers interpretedas remnants of the extinct Kula (or Resurrection) plate. ContinentalMoho just north of this underplated stack is more than 55 kmdeep. Near the Arctic margin, the Brooks Range is underlainby large-scale duplex structures that overlie a tectonic wedgeof North Slope crust and mantle. There, the Moho has been depressedto nearly 50 km depth. In contrast, the Moho of central Alaskais on average 32 km deep. In the Paleogene, tectonic underplatingof Kula (or Resurrection) plate fragments overlapped in timewith duplexing in the Brooks Range. Possible tectonic modelslinking these two regions include flat-slab subduction and anorogenic-float model. In the Neogene, the tectonics of the accretingYakutat terrane have differed across a newly interpreted tearin the subducting Pacific oceanic lithosphere. East of the tear,Pacific oceanic lithosphere subducts steeply and alone beneaththe Wrangell volcanoes, because the overlying Yakutat terranehas been left behind as underplated rocks beneath the risingSt. Elias Range, in the coastal region. West of the tear, theYakutat terrane and Pacific oceanic lithosphere subduct togetherat a gentle angle, and this thickened package inhibits volcanism.