The structure of interannual rainfall variability is examined using a rotated principal components analysis applied to summer seasonal rainfall averages across a domain consisting of AZ, NM, and portions of UT, CO, and TX. Three distinct subregions together account for a large fraction of the total interannual variance of summer rainfall across this domain: (1) the western portion of the domain, consisting of AZ and southern UT; (2) western and central NM; (3) eastern NM and western TX. The interannual time series of expansion coefficients for these regions are linked to different processes and moisture sources (including sea surface temperatures and spring snow cover) and that modulate summer rainfall across the American Southwest