Thesis (Ph.D., Natural Resources)--University of Idaho, June 2014 | Abies grandis and Abies concolor occupy many of the forests of western North America and are of great ecological and economic importance to the region. Abies grandis is generally a seral component of mesic, low to mid elevation forests of the Pacific Northwest and the northern Rocky Mountains with a mild maritime climate. Abies concolor is generally a dominant tree of much more xeric, mid to high elevation forests of the central and southern Rocky Mountains with a few small populations in the mountains of northern Mexico. Although these taxa are regarded as ecologically, morphologically and genetically distinct in these regions, they form an expansive hybrid zone in between from the Transverse Range in southern California to the north-central Cascade Mountains of Washington State and the Mountains of north-central Idaho. Due to the complex geographic and ecological patterns of phenotypic and genetic variation of these populations, their description, identification, delineation and taxonomic treatment remain largely unresolved. In this study, molecular genetic and morphometric analysis are used to determine the paternal and maternal lineage and genetic composition of hybrid and pure populations across the entire geographic region. Additionally, analysis of GIS-based environmental data layers is used to assess the differences that characterize the environmental niche of pure and hybrid populations. These results should inform a more uniform taxonomic treatment and facilitate further genetic and ecological study of this complex.