We measure seismic attenuation beneath North America using waveform cross-correlation and cluster analysis, and obtain images of the laterally varying anelastic structure of the upper mantle. Cluster analysis improves attenuation measurements by systematically comparing only highly similar waveforms, which reduces bias from scattering, directional differences in source functions, and source-side structure. While lacking station coverage in many areas, the P- and S-wave results are correlated (R2 ≥ 0.5) in both travel time and attenuation. Much weaker correlations are observed between travel-time and attenuation measurements. Similarities and differences between attenuation and travel times may be used to infer the source of the observed anomalies. The observed anelastic structure has a long-wavelength pattern crudely similar to that of seismic velocity, which likely indicates higher temperatures beneath western North America than in the east. Shorter-wavelength structure suggests complex variations requiring alternate explanations such as variable water content.