Seismograms recorded at an array of 10 closely spaced seismometers in the western United States are stacked about the ScP phase and display a complex set of phase arrivals in addition to ScP. One dimensional forward modeling with ultra-low velocity zone structures are unable to match the observed waveform. Forward modeling with core-rigidity zone structures, where S-waves can propagate in a thin layer below the core-mantle boundary, provide reasonable waveform fits to the largest amplitude phases. The basic core-rigidity zone model has thickness of 1.1 km, shear wave velocity of 1.8 km/s, and density decrease of 10%, although tradeoffs in model parameters are observed. Waveform fits are insensitive to small changes in P-wave velocity in the core-rigidity zone. To match trailing smaller amplitude phases, S-wave multiples are modeled in the core-rigidity zone. Cross correlation of ScP waveforms from 392 EarthScope seismometer sites surrounding the small array site shows discrete patches of similarity to the above model. These results point to a spatially large but patchy core-rigidity zone beneath Mexico and adds to the small set of previous core-rigidity zone observations globally.