Mean water vapor fluxes for the July-August period have been calculated using 9 years of mostly twice-daily radiosonde observations from southwestern North America. These results have been merged with mean radiosonde observations from several other sites of shorter duration. The results show that there is a maximum northward moisture flux at the northern end of the Gulf of California; this flux is strongest at levels below 700mb. The diurnal cycle of the moisture flux is shown for one site along the Gulf of California and the need to resolve the diurnal cycle of the windfield over the region is stressed. The mean fluxes from radiosonde observations have been compared with fluxes from other published analyses using global analyses. Major differences are apparent, with the present study showing larger northward fluxes. However, moisture fluxes calculated from mesoscale model output also seem unable to capture certain characteristics of the flux field over the Gulf of California. Some of the main differences are highlighted.