The range and habitat affinities of the rock vole (Microtus chrotorrhinus, Rodentia, Muridae) have been enigmatic, especially at the western margin of its range, a problem made more difficult because the species is rare or uncommon throughout its range. We recorded rock voles at 53 new sites in northern Minnesota and observed broader habitat associations than the boulder fields and talus commonly reported. The distribution in Minnesota corresponds to the Vermilion ground moraine of the Rainy lobe of the Pleistocene late Wisconsinan glaciation, a striking association of a mammalian species range limit with a geological feature other than a local geosite.