This study investigated the use of x-ray emission spectroscopy as a means of determining the total rubidium and strontium contents of minerals and hence of determining the apparent age of these minerals. Fifty minerals collected from pegmatite dikes associated with the Southern California batholith in the Peninsular Range province of southern California and northern Baja California were selected for analysis. Each sample was digested in hydrofluoric acid and then analyzed with a General Electric XRD-5 spectrometer, using a topaz analyzing crystal and 0.005 inch Soller slit for spectrum analysis. Rubidium peak and rubidium background positions were scaled for 400 seconds each, while the strontium peak and four strontium background positions were scaled for a total of 8000 seconds each. The scaled number of counts were normalized with respect to a standard scaled during the mid-point of each sample run to minimize the effects of instrumental drift. Of the fifty mineral specimens studied, some thirty-four proved suitable for age determination. The mean age of the thirty-four, 102 million years, agrees, within the experimental error, with the results of previous determinations made by other investigators. The x-ray fluorescence method, as compared to isotope dilution, eliminates all chemical procedures, is non-destructive to the specimen and requires about one-half day for a complete analysis, instead of several days.