The southern Alaskan margin captures a transition between compression and strike-slip-dominated deformation, accretion of the overthickened Yakutat terrane, termination of Aleutian arcmagmatism, and the enigmatic Wrangell Volcanic Field. The extent of subduction and mantle structurebelow this region is uncertain, with important implications for volcanism. We present compressional andshear wave mantle velocity models below south central Alaska that leverage a new seismometer deploymentto produce the most complete image of the subducting Pacific-Yakutat plate to date. We image a steeplydipping slab extending below central Alaska to >400 km depth, which abruptly terminates east of ~145°W.There is no significant slab anomaly beneath the nearby Wrangell volcanoes. A paucity of volcanism isobserved above the subducting Yakutat terrane, but the slab structure below 150 km depth andWadati-Benioff zone here are similar to those along the Aleutian-Alaska arc. Features of the mantle wedge oroverlying lithosphere are thus responsible for the volcanic gap.