The deployment of a two-dimensional array of broadband seismometers during the PASSCAL Rocky Mountain Front experiment produced a teleseismic and regional event data set which provides constraints on both the laterally averaged and laterally varying structure of the crust and upper mantle beneath the Southern Rocky Mountains and Great Plains. Results from a spectrum of seismological imaging and inversion techniques indicate that the western edge of the North American tectosphere has been relocated from its position beneath the Paleozoic passive margin to a position several hundred kilometers east of the Colorado Front Range. The mantle and crustal structure presently beneath the Colorado Rockies suggest a laterally variable dynamic state, which, on average, must provide partial support for the high topography.