The systematic status of the populations of lizards assignable to _Cnemidophorus sacki_ in western México (Sonora southward to Jalisco) has been reviewed in detail by Zweifel (1959, Bull. Amer. Mus. Nat. Hist, 117 (2):57-116), who stated that the use of the specific name _sacki_ for the western populations rests upon a reasonable, but as yet unproved, assumption that intergradation occurs. Although Zweifel examined specimens of the nominal subspecies from the upper Balsas Basin, he did not study specimens from the intervening area–the Tepalcatepec Valley in Michoacán.

Field studies and the examination of large series of preserved specimens of _Cnemidophorus_ from the Tepalcatepec Valley show the presence of _Cnemidophorus sacki_ in the region between the ranges of _C. sacki sacki_ in the upper Balsas Basin and _C. sacki occidentalis_ in Jalisco and southern Nayarit. Furthermore, the populations of _sacki_ inhabiting the Tepalcatepec Valley have characters of scutellation and coloration that distinguish them from other described subspecies of _sacki_.