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Univariate and multivariate statistical methods were used to examine geographic variation in skull and horn characters of 694 bighorn sheep (Ovis canadensis) specimens from the Great Basin north to British Columbia and Alberta to test previous taxonomic hypotheses, Substantially more morphometric variation in skull and horn size and shape was found west of the Rocky Mountains than within the Rocky Mountains. Our results did not support the recognition of Audubon’s bighorn sheep (O. c. auduboni) as a subspecies separate from Rocky Mountain bighorn sheep (O. c. canadensis). California bighorn sheep (O. c. californiana) from Washington and British Columbia were not distinguishable from Rocky Mountain bighorn sheep but differed notably from populations in the Sierra Nevada considered part of that subspecies. Extirpated native populations from northeastern California, Oregon, and southwestern Idaho, also considered to be O. c. californiana, shared with Nelson bighorn sheep (O. c. nelsoni) from the Great Basin desert a horn-related character that distinguished them from Rocky Mountain bighorn sheep. Bighorn sheep from the Sierra Nevada were found to be distinguishable from those of the adjacent Great Basin region. Our morphometric results were concordant in geographic patterns with mtDNA data. We synonymize O. c. auduboni with O. c. canadensis. We also assign extant and extinct native populations of O. c. californiana from British Columbia and Washington to O. c. canadensis. Finally, we assign the extinct native populations of O. c. californiana from Oregon, southwestern Idaho, northern Nevada, and northeastern California to the Great Basin Desert form of O, c. nelsoni, recognizing that some transition to Rocky Mountain bighorn sheep probably occurred along that northern boundary. With these taxonomic revisions, the range of O. c. californiana includes only the central and southern Sierra Nevada.