Natural History of the Ground Squirrels of California/Rock Squirrel
ROCK SQUIRREL.
Citellus variegatus grammurus (Say).
Other names.—Plateau Ground Squirrel; Rocky Mountain Ground Squirrel; Citellus grammurus.
Field characters.—As for the Beechey Ground Squirrel, differing in longer tail and grayer general coloration; fore parts of body continuously grayish white, without specially set-off shoulder patches. Length of body alone about 10½ inches, with tail about 8 inches more.
Description.—Summer pelage: Head dull buckthorn brown, grizzled on cheeks and sides of snout; eyelids dull white; whiskers black; backs of ears dull buffy brown, insides of ears pinkish buff. Forward half of upper surface of body light gray, with decided dusky mottling in transverse trend; hinder half of upper surface, of a tawny-olive tone, lighter on sides, and with similar transverse mottling. Whole lower surface of body and upper surfaces of feet, pale pinkish buff, nearly white in some specimens; belly with grayish bases of hairs showing through. Tail considerably bushier than in beecheyi, as well as being longer; length of hairs up to 50 mm. (2 inches); tips of hairs more extensively white, thus nearly as in douglasii; dark and light intervals on individual hairs same as in beecheyi, that is, three dark and four light, the latter including the tipping.
Color variations.—Wear and exposure to intense sunshine evidently accounts for the yellowing of the pelage of one specimen at hand; also the tail of the animal shows a curious crinkling of the hairs as if scorched. An adult of date June 2 has the forward half of the body in fresh new (summer) pelage; this is relatively harsh in texture, without underfur. Young less than half grown are colored almost exactly as described above for adults, but the pelage on the under surface is very scanty, so that the bare skin shows through extensively. No winter specimens are at hand from within the state of California.
Measurements.—Only two adult specimens are available from California. These are from the Providence Mountains, eastern San Bernardino County, and show measurements, in millimeters, as follows: Male and female (nos. 117301 and 117300, respectively, Biol. Surv. coll., U. S. Nat. Mus.): Total length, 470, 465; tail vertebræ, 194, 205; hind foot, 58, 54; ear from crown, 20, 21; greatest length of skull, 61.2, 58.4; zygomatic breadth, 38.5, 37.0; interorbital width, 15.4, 14.2.
No skull differences of crucial importance between grammurus and beecheyi are apparent to us in the material at hand for study.
Type locality.—Purgatory River, near mouth of Chacuaco Creek, Las Animas County, Colorado (according to Cary, 1911, p. 87). This form was originally described by Thomas Say in 1823.
Distribution (in California).—Inhabits the Providence Mountains, in eastern San Bernardino County (see fig. 17); also "the canyons of the Colorado River" (Merriam, 1910, p. 2). Life-zone chiefly Upper Sonoran.
Specimens examined from California.—A total of five, all collected by Frank Stephens, June 1 to 3, 1902, in the Providence Mountains, 5,000 to 5,500 feet altitude. These were loaned us from the Biological Survey collection, United States National Museum.
The Rock Squirrel is really a very close relative of the Beechey Ground Squirrel and its habits are doubtless closely similar. It is a wide-ranging form through the southern Rocky Mountain region, stations of occurrence in southeastern California being merely far western outposts. Two of the specimens from the Providence Mountains are young less than half grown; these were taken on June 1, and indicate a breeding date at about the same time of year as for other ground squirrels in the upper Sonoran zone.