Although the deployment of the US Array transportable array has enabled numerous discoveries about the crust and upper mantle, previous studies have lacked the resolution to track major discontinuities in detail. This study employs the global phase PKIKP for use in P-wave reflection analysis to improve the resolution of the Mohorovičić discontinuity and lithosphere-asthenosphere boundary (LAB) and evaluate their relationship with surface geology and physiography. The results reveal striking detail of both shallow geologic structures and the major discontinuities. We observe crustal thickening below the central and southern Appalachian Mountains and develop a new criterion for mapping the LAB based on increased reflectivity resulting from inferred drag-induced flow in the upper asthenosphere. This new criterion increases the traceability of the LAB beneath heterogeneous lithospheric settings and provides clarity on the nature of plate motion over the asthenosphere.