Here we present a 3D shear velocity model for the lower crust and upper mantle beneath the Great Plains in the central United States using finite frequency Rayleigh wave tomography. We use USArray Transportable Array recordings of teleseismic Rayleigh waves and first invert for phase velocity using the two-plane wave method with finite frequency kernels, then invert the resulting dispersion curves for shear velocity structure. We characterize the lithospheric structure in this tectonically transitional regime to illuminate the differences between the actively deforming west and stable continental interior. The west is defined by slow velocities and thin lithosphere, whereas the east has fast velocities and thick lithosphere, with the thickest lithosphere under the Superior craton. From our tomography and heat flow data, we infer warm temperatures in the west and suggest that the asthenospheric mantle contributes to anomalously high elevation in the west with secondary contributions from crustal effects.