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We evaluated the effects of nitrogen fertilization on species composition on grazed annual rangeland in California. Treatments included rates of 30 and 60 pounds of actual nitrogen in the form of ammonium sulfate, combined with seasonal timings of fall and early spring. Treatments were applied during the 2012/2013 growing season at three different locations and then monitored the following spring in 2014. Each experimental site was grazed, though small differences in grazing strategy existed. Analyzed with all three sites combined, all treatments reduced medusahead (Taeniatherum caput-medusae) composition (P=0.01) except for the lowest rate applied in the fall. No significant difference in medusahead existed between the two higher rates and the lower rate applied in the spring which had a mean of 15% medusahead basal cover, as compared to the control at 23% basal cover. The lower rate applied in the fall had 18% medusahead likely having some reduction in medusahead, but not significantly reducing basal cover. All treatments, ranging from 28-32% basal cover, had significantly higher filaree (Erodium spp.) over the control at 22% (p<0.01), with no difference between treatments. Slender oat (Avena barbata Link) basal cover was only increased in the two lower rate treatments (P<0.01), though this increase was only from one to five and six percent. Interestingly the two fall treatments reduced medusahead from six to three percent, with no difference between the control and the two spring treatments. When comparing all three sites little or no difference was seen in annual ryegrass (Lolium multiflorum), native wildflower species, soft brome (Bromus hordeaceus L.), catsear (Hypochaeris radicata), hare barley (Hordeum murinum), or bare ground, though differences did exist at individual sites.