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The Mojave Neovolcanic Province (MNVP), located in the Mojave block of southern California, comprises late Miocene to Quaternary small-volume basaltic centers. Geochemistry indicates an asthenospheric source for the MNVP beginning in the late Miocene, but no physical evidence of missing mantle lithosphere has been presented. We utilize receiver functions and ambient noise tomography to image the lithosphere beneath the Mojave block. Regionally, we find thin crust that thickens distal to sites of MNVP volcanism. Shear wave velocities between 40 and 75km depth are consistent with the presence of mantle lithosphere in the southern Mojave block and very thin or missing mantle lithosphere to the north. With one exception, MNVP volcanoes lie along this sharp boundary. Our observations, together with the established geologic history and geochemistry of the MNVP, can be explained by small-scale edge-driven convection producing ongoing lithospheric removal within the Mojave block. Our results provide another example of lithospheric instability that occurs in response to rapid changes in mantle dynamics induced by major changes in tectonic plate geometry.