The Columbian ground squirrel (Spermophilus columbianus (Ord)) is represented by two recognized subspecies, S. c. columbianus (Ord) and S. c. ruficaudus (A. H. Howell), that occupy allopatric but adjacent geographical areas in Washington, Oregon, and Idaho. Since numerical cranial characteristics of these subspecies have not been documented, we measured 8 cranial characteristics on 94 adult and 32 juvenile Columbian ground squirrels in an area considered to be occupied by S. c. columbianus. Body weights and standard body measurements were recorded for adults and juveniles. The study area included portions of the River of No Return Wilderness Area in central Idaho. Howell's (1938) original descriptions seemed to differentiate S. c. ruficaudus from our sample of Columbian ground squirrels. Juvenile Columbian ground squirrels did not attain full cranial development until their second season. Length of maxillary tooth row in juveniles, especially females, may closely approximate adult dimensions by the end of their first summer.
Elliott, Charles L. and Flinders, Jerran T.
"Cranial measurements of the Columbian ground squirrel (Spermophilus columbianus columbianus), with special reference to subspecies taxonomy and juvenile skull development,"
Great Basin Naturalist: Vol. 44
, Article 18.
Available at: http://scholarsarchive.byu.edu/gbn/vol44/iss3/18