Technical Abstract: The relationship of geographic origin and genetic identity was determined by DNA fingerprinting 25 mountain brome (Bromus carinatus Hook. & Arn. sensu lato [Poaceae]) seed accessions that originate from widely dispersed sites throughout western North America. A high degree of genetic identity was detected within accessions, which probably reflects uniformity within natural populations. Moreover, four well-defined genetic groups encompassed all but five of these accessions. Samples from two of these groups had restricted geographic range. However, two other well-defined genetic groups had broad overlapping geographical ranges, which also included other genotypes. California produced the greatest diversity of genotypes. Excluding comparisons within accessions, the overall correlation of genetic similarity and geographic distance among accessions was weak. These patterns of genetic variation are observed in self-pollinating plant species. This study identified at least one well-defined group of genotypes that is naturally abundant and widely dispersed throughout the western United States.