This paper focuses primarily on the effect of El Niiio on seasonal and annual precipitation at 26 locations in Arizona and western New Mexico for an 86-year period from 1900. Following Rasmusson (1984, each year is classified as either a non-El Niiio year (51) or an El Niiio year (33, with the El Niiios designated as being very weak (4), weak (8), moderate (12), or strong (1 1). Using the Mann-Whitney U-test for the 19 stations in Arizona, we find that, in the spring (March-May) and in the autumn (September-November), there is a positive relationship between precipitation in Arizona and both moderate and strong El Niiios.These results are verified by correlating seasonal and annual precipitation for the complete 26-station network with the pressure difference between Tahiti and Darwin. Plausible physical explanations for these results are given.