This thesis presents a new 3-D shear velocity (Vs) model of the lithospheric structure beneath the Colorado Plateau and its surrounding regions to understand the complicated lithospheric modifications caused by major Cenozoic tectonic and magmatic activities. Prior to this work, lack of an overall velocity model had prevented a comprehensive understanding of the current encroachment patterns near the margins, and of the perplexing crust/mantle boundary beneath the plateau. Using the new USArray data, I have inverted the isotropic Vs model from the Rayleigh wave dispersion curves obtained by a modified two-plane wave method. The resulting Vs structures not only clearly image the sublithospheric low-velocity channels, but also identify the high velocity anomalies underlying the western plateau for the first time in surface wave tomography to support the recent delamination hypothesis. This work also provides a high-resolution velocity model for geodynamic modeling on lithosphere-asthenosphere interactions.