Fieldwork was carried on by the California Museum of Vertebrate Zoology during 1917 in the Inyo region of eastern California. In going over the collection of birds obtained, the attention of the writer was arrested by certain peculiarities evident in the Mountain Chickadees. Comparison with series from the Sierras showed the Inyo birds to be paler colored and longer tailed; and in order to appraise these differences in taxonomic terms it became necessary to assemble material representative of the entire range of the species, in so far as possible. The results of the study thus undertaken are presented herewith.