The Colorado Plateau-Great Basin (CPGB) PASSCAL experiment provides broadband seismic data that allow us to determine crustal and upper mantle structure in the Colorado Plateau and eastern Great Basin. Twelve portable broadband seismometers throughout Utah and Nevada are supplemented by permanent broadband stations in the region. Receiver functions indicate an average crustal thickness of 35¿5 km in the Great Basin (GB) with a strong P-to-S (Ps) conversion from the Moho. The crust in the transition between the Great Basin and Colorado Plateau (CP) produces a strong intracrustal conversion. The CP has somewhat thicker crust (42¿5 km) and weaker Moho conversion. BR surface wave phase velocities are 3--4% higher than CP phase velocities in the 20--35 s range, consistent with a thinner crust under the GB. The phase velocities at periods greater than 40 s are indistinguishable between the two provinces, indicating that differences between upper mantle velocities are minor. Shear wave splitting yields fast polarizations that parallel the western and northern boundaries of the CP, with delay times decreasing towards the center of the Plateau.¿ 1997 American Geophysical Union