Geomys is common in Pleistocene deposits, especially on the Great Plains. Certainly the center of differentiation for Geomys was in this region, although at times, probably when conditions were favorable, Geomys expanded its range into adjacent areas, reaching the Pacific Coast in Irvingtonian times and the Atlantic Coast at the time of the Illinoian glaciation. The earliest Pleistocene records of the genus are from the Great Plains. McGrew (1944:49) described Geomys quinni from the Sand Draw local fauna, Brown County, Nebraska, considered by Hibbard (1958:11) to be Nebraskan in age. As mentioned in the account of Pliocene geomyids, Geomys quinni occurs also in the late Pliocene deposits of southwestern Kansas. Also, Geomys quinni occurs in the Broadwater-Lisco local fauna of Morrill and Garden counties, western Nebraska (Barbour and Schultz, 1937:3; Schultz and Stout, 1948:560-563; Schultz et al., 1951: table 1). The Broadwater-Lisco is currently regarded as Aftonian deposits (Schultz and Stout, loc. cit.; Hibbard, 1958:11). Hibbard (1956:174) identified Geomys quinni from the Deer Park local fauna, probably deposited during the early Aftonian interglacial, of Meade County, Kansas. Strain (1966:36) described Geomys paenebursarius on the basis of fossils obtained from early Pleistocene deposits of the Hudspeth local fauna from western Hudspeth County in the Trans-Pecos of Texas. The Hudspeth fossils were probably deposited during the Aftonian interglacial. From Kingman County, Kansas, Hibbard (op. cit.: 164) recovered isolated teeth of Geomys from the Dixon local fauna, regarded by him (op. cit.:153-154) as deposited during the latest Nebraskan glaciation, and correlated by him with the Sand Draw local fauna of Nebraska. Hibbard (1958:11) later regarded the Dixon as a transitional fauna between Nebraskan and Aftonian. The remains of Geomys from the Dixon are known only from isolated teeth. The teeth are small, and suggest that a smaller species of Geomys may have occurred along with the more common and larger G. quinni during the early Pleistocene (see discussion beyond of the Saunders Geomys). Geomys quinni was widespread and common throughout the central Great Plains from the late Pliocene (Rexroad fauna) through the early Pleistocene (Nebraskan and Aftonian deposits).
Hibbard (1956:179) referred the pocket gopher remains taken from the Saunders local fauna in Meade County, Kansas, to Geomys tobinensis, a small species having continuous enamel bands around the lower premolar in younger specimens. The Saunders local fauna was deposited in the late Aftonian and is younger than the Deer Park local fauna discussed above. Paulson (1961:138) later pointed out that the Saunders Geomys is distinct from Geomys tobinensis; hence, the small pocket gopher from the Saunders local fauna is probably an unnamed species, perhaps more closely allied to paenebursarius than to quinni. The small Geomys reported from the Aftonian Broadwater-Lisco local fauna of Nebraska (Schultz and Stout, 1948:563) may also be the same as the Saunders pocket gopher, but the smaller adult specimens occurring in the same bed with larger specimens probably are females and the larger specimens males. In all living Geomyini females have smaller skulls than males.
The Irvingtonian provincial age is currently regarded as Middle Pleistocene and includes the late Kansan glaciation (that part occurring after the glacial maximum) and the Yarmouthian interglacial (see Hibbard et al., 1965:512-514). The Irvingtonian provincial age, therefore, follows the late Blancan provincial age of the early Pleistocene and is succeeded by the Rancholabrean provincial age of the late Pleistocene. No specimen of an Irvingtonian Geomys is referable to any living species. Two Irvingtonian species have been described. Hibbard (1944:735) named Parageomys tobinensis [= Geomys tobinensis] from the Tobin local fauna of Russell County, Kansas. This species since has been reported from the Cudahy local fauna of Meade County, Kansas (Paulson, 1961:137). Hibbard (1956:183) also identified as Geomys tobinensis the pocket gopher recovered from the Saunders local fauna, a late Aftonian deposit of Meade County, Kansas, and reduced the technical name Parageomys from generic to subgeneric rank. Paulson (op. cit.:138) pointed out that the Saunders specimens differ from G. tobinensis, and he, therefore, restricted the name to the small Geomys of the Cudahy and Tobin local faunas of Irvingtonian provincial age. G. tobinensis is markedly smaller than the Blancan G. quinni. The Cudahy and Tobin local faunas are of approximately the same age, and presently both are included in one unit, the Cudahy fauna. The Cudahy fauna is considered to have been deposited in late Kansan as it occurs in strata immediately below the Pearlette ash.
Recently, White and Downs (1961:8) described a new Irvingtonian species, Geomys garbanii, from the middle Pleistocene Vallecito Creek local fauna of San Diego County, California. Many well preserved fossils of the new species were recovered. Geomys garbanii is of medium size (approximately the size of one of the larger subspecies of G. bursarius), and significantly larger than the Irvingtonian Geomys tobinensis of the Great Plains. The Vallecito Creek occurrence of Geomys is the first authenticated record from the Pacific Coast region. Matthew (1902:320) erroneously referred remains of Thomomys to the genus Geomys in his revised list of Cope's earlier report on the Fossil Lake (or Silver Lake) fauna (see discussion of Thomomys above).
A number of Irvingtonian fossil remains of Geomys have not been identified with particular species. Hibbard (1941a:206) found Geomys in the Borchers local fauna (deposited in the time of the Yarmouthian interglacial) of Meade County, Kansas. Also, Geomys has been reported from several sites in Nebraska. Schultz and Tanner (1957:67) reported Geomys from the Angus fossil quarry in Nuckolls County, south-central Nebraska. The Angus fossils were found in sediments of the Sappa Formation considered by Schultz and Tanner to be a Yarmouthian deposit. Fossil quarries (Hay Springs, Rushville, and Gordon) along the south side of the Niobrara River Valley in Sheridan County, Nebraska, have also provided records of geomyids. Both a large and small species of Geomys have been reported from the more recently excavated Rushville and Gordon sites (Schultz and Stout, 1948:562-567, and table 3). In view of the great disparity in size owing to sex, these may actually be males and females of the same species, as mentioned above. The name Hay Springs has been used in reference to all three sites. The ages of the Hay Springs sites are approximately the same, but their correlation is presently under debate. Schultz and Tanner (1957:68-71) maintain that the fossils are distinctly middle Pleistocene, and that they were deposited during late Kansan glaciation, or perhaps from early Yarmouthian into early Illinoian, with the largest concentration coming from the Sappa sands of pre-Illinoian (Yarmouth) age. Hibbard (1958:25), basing his opinion on the presence of Microtus pennsylvanicus, and the stage of evolution of other species in the assemblage, regards the Hay Springs sites as probably Illinoian deposits, but certainly no older than that.
Mooser (1959:413) identified as Geomys the pocket gopher from Irvingtonian deposits in Arroyo San Francisco (loc. no. 5) near the city of Aguascalientes, México. As suggested elsewhere in this account, these fossils may be referable to Zygogeomys rather than Geomys. The Irvingtonian provincial age of this fauna was established by Hibbard and Mooser (1963:245-250). Other alleged occurrences have recently been compiled by Alvarez (1965:19-20). Maldonado-Koerdell (1948:20) noted four fossil occurrences of the genus Geomys in México. Two of these from San Josecito Cave in Nuevo León have since been identified with the genera Orthogeomys and Pappogeomys (Russell, 1960:543-548); the third listed by Maldonado-Koerdell from "near Ameca, Jalisco," was based on Brown's (1912:167) mention of some bones supposedly of the family "Geomyidae," and the fourth refers to pocket gopher remains from the "Hochtals von Mexiko" listed as Geomys by Freudenberg (1921:139). His generic identification is doubtful and the specimens should be compared with Mexican genera of the Geomyinae.
Upper Pleistocene records of Geomys also are common. Upper Pleistocene is here understood to include late Illinoian, Sangamon and Wisconsin deposits; all are considered to be of Rancholabrean provincial age (see Hibbard et al., 1965:512-515) and post-Irvingtonian. The presence of remains of Bison and/or Microtus pennsylvanicus are currently considered mammalian index fossils of Rancholabrean faunas. In the Illinoian, Geomys extended its range to the Atlantic Coast in the southeastern United States. The eastern and western species-groups evidently were isolated throughout much of the late Pleistocene, and, therefore, evolved separately. Of the two, the eastern, or pinetis, species-group seems to have remained somewhat more generalized, and the western, or bursarius, species-group has become more specialized. The Rancholabrean Geomys from deposits in the southeastern United States are referable (see Ray, 1963:325) to Geomys pinetis.
Marsh (1871:121) described Geomys bisulcatus from the North Prong of the Loup River (near Camp Thomas), Nebraska. These beds are also termed the Loup Fork or Loup River fossil beds (see discussion on [p. 485]), and they lie along the upper reaches of the Middle Loup River in Thomas County (near Senea), Hooker County (near Mullen), and southeastern Cherry County (probably the North Prong beds northwest of Mullen). These beds were at first thought to be of Miocene age, but later were regarded as early Pliocene (see Schultz and Stout, 1948:562-566 for a historical account of expeditions to these fossil sites). Schultz and Tanner (1957:71-72) pointed out that the principal fossiliferous beds in the Middle Loup region are of middle to late Pleistocene age, with most of the fossils coming from the Crete sand and silt beds which are probably early Illinoian deposits, and, therefore, younger than the Hay Springs faunas. Some fossils may have come from the Sappa deposits dated by Schultz and Tanner (loc. cit.) as mostly Yarmouthian deposits. Geomys bisulcatus, judging from the original description and Hibbard's discussion of the cotypes (1954:357), does not differ significantly from Geomys bursarius. However, Geomys bisulcatus is tentatively retained as a valid species. Based on the evidence cited above it seems unlikely that Geomys bisulcatus occurred in pre-Irvingtonian times as often suggested in the literature.
The genus Geomys has been identified in several faunas of Illinoian age, all from the Great Plains. Stephens (1960:1961) reported the genus from the Doby Springs local fauna in Harper County, Oklahoma, and Starrett (1956:1188) reported it from the Berends local fauna in Beaver County, Oklahoma. Schultz (1965:249) assigned 21 isolated teeth, including six incisors, from Butler Springs local fauna (considered by him to be late Illinoian, following the glacial maximum) to Geomys cf. bursarius. Hibbard and Taylor (1960:167) reported a baculum tentatively identified as that of Geomys from the early Illinoian Butler Springs local fauna (including the Adams fauna) of Meade County, Kansas. Hibbard (1963:206) recorded the genus Geomys from the Mt. Scott local fauna (late Illinoian deposits) of Meade County, Kansas; the specimens probably are referable to the living species bursarius. From McPherson County, Kansas, Hibbard (1952:7) reported the genus Geomys from the Kentuck Assemblage, which he (1958:25) regarded as a composite of Illinoian and Sangamon species. Specific identification of the Illinoian pocket gophers is uncertain, primarily due to the fragmentary nature of the material. On the basis of dental characters alone most specimens could be referred to G. bursarius; however the taxonomic status of G. bisulcatus is in doubt, and more complete material may indicate that the Illinoian gophers are specifically distinct from the living species. Consequently, most authors, including myself, have made no attempt to refer these specimens to species. Nevertheless, the Illinoian Geomys from the Great Plains is more closely allied to the living species of Geomys than it is to the earlier Irvingtonian species.