Since its origin, the Grand Canyon of the Colorado River has provided an effective barrier, isolating the Kaibab squirrels on the north rim from the Abert squirrels on the south rim. The differences in these squirrels have been used as a classical example of the role of geographical isolation in evolution. This paper examines the differences in the two populations and describes the nature and extent of the isolating mechanism. It then evaluates the applicability of the violations of restrictions of the Hardy-Weinberg equilibrium population. The study concludes that the Kabab squirrel populations should be an ideal test group for assessing the extent of changing gene frequencies across the uniformitarian time scale claimed for the formation of the Grand Canyon. Evidence is presented showing violations of all of the Hardy-Weinberg restrictions for an equilibrium population but with only minute differences between the two populations. This does not correlate well with the standard explanation for the time of formation of the isolation barrier. It is suggested that these data provide indirect evidence for a very recent origin of the Grand Canyon.