A new compressional velocity profile for the western or tectonically active portion of the United States has been constructed by matching long-period body wave forms with synthetic seismograms. The wave form data come from shallow California earthquakes with very well constrained source mechanisms. The known source pulses from the events were convolved with delta function responses for velocity models computed by using a Cagniard-deHoop algorithm to produce the synthetic seismograms. By using this technique it was possible to identify and model strong arrivals from both upper mantle velocity discontinuities in the wave form data. The new model fits the travel time, dT/dΔ, and short-period wave form data as well as or better than the velocity profile previously proposed for the region. Nonetheless, it is basically simpler in form than this earlier model. Below the low-velocity zone the velocity gradients are very nearly linear with depth, and the two discontinuities are simple first-order jumps. The first discontinuity occurs at 400-km depth and entails a 5% velocity jump, and the second occurs at 670 km, entailing a 4% jump. The velocity inflection near 550 km has been eliminated.