Page:Natural History of the Ground Squirrels of California.djvu/17

Rh compared with total length of skull), broadest jugals, stoutest postorbital processes, highest developed sagittal crest, most nearly approaching parietal ridges (these meeting also farthest forward), and broadest frontal region (which also shows a concave or "dished" upper surface). In other words, old animals have skulls which are more massive and angular than those of young ones. We find that relative age of an individual can be recognized approximately by the relative degree of development of the above characters. Amount of wear on the crowns of the molariform teeth and of advance in coalescence of the contiguous bones along certain sutures also give criteria for determination of age.

Weights.—Average and extreme weights, in grams, of twenty full-grown specimens from west-central California are as follows: Ten males, 696 (600–923); ten females, 592 (491–774). Averages in ounces: males, about 24 (1½ pounds); females, about 20 (1¼ pounds).

It appears that males are 17 per cent heavier than females. The heaviest specimen out of a total of 36 weighed, was an old male tipping the scales at 923 grams, or 32½ ounces, or a trifle over two pounds. This animal was shot June 12, 1918, in a slaughter yard at Mendota, and was exceedingly fat.

Type locality.—"Neighborhood of San Francisco and Monterey" (Richardson, 1829, p. 170).

Distribution area.—The greater part of central and southern California west of the desert divides. Altitudinally, ranges from sea-level up regularly to about 6,000 feet, and locally and sparsely to as high as 8,200 feet (in Yosemite National Park). As regards life-zone, the California Ground Squirrel is most abundant in the Upper Sonoran zone, less so in the Lower Sonoran and Transition, and but relatively rare and local in Canadian (see fig. 23).

More in detail, this squirrel is limited to the northward in the coast belt abruptly at the south sides of the Golden Gate, San Francisco Bay, Carquinez Strait, and Suisun Bay. Its range extends northward over the eastern half of the Sacramento Valley to the Marysville Buttes and its limits thence swing northeastwardly through the Feather River country to the southern border of Lassen County. From this last point south it covers both slopes of the Sierras nearly to the Yosemite region, but thence south to Tulare County, only the western slope. In the vicinity of Lake Tahoe it gets a little way into the state of Nevada. To the southward it covers most of the San Joaquin Valley, and the coast belt south throughout the San Diegan district to the Mexican border, and beyond this even to the San Pedro Martir mountains.

Along the eastern border of its range, from Tulare County south to Riverside County, the race beecheyi grades into the race fisheri. The dotted line on the map (fig. 17) marks approximately the center of the area of intergradation between the two races. As will be seen, the limits of beecheyi swing west across the southern San Joaquin Valley and thence around south so as to exclude the Bakersfield region and the Tehachapi, Tejon, San Bernardino and San Jacinto mountains.

Specimens examined.—A total of 149 specimens from the following localities in California: San Francisco County: Ingleside Race-track, 1. Alameda County: vicinity of Berkeley, 9. Contra Costa County: Walnut Creek, 12; west side Mount Diablo, 2. San Mateo County: Sierra Morena, 1; Pescadero Creek, 1. Santa Clara County: Palo Alto, 1. San Benito County: Cook, 2. Monterey County: Monterey, 6. Sutter County: Marysville Buttes, 2. Stanislaus County: Claribell Station, 1. San Joaquin County: eight miles southwest of Tracy, 1. Sierra County: near Sierraville, 1. Placer County: Dutch Flat, 1; Blue Canyon, 1; Cisco, 2. El Dorado County: Fallen Leaf Lake, 1; Kyburz Station, 2. Tuolumne County: Aspen Valley, 6,400 ft., 1. Mariposa County: Merced Grove, 1; Crane Flat, 6,300 ft., 1; Indian Creek, 6,100 ft., 1; Yosemite Valley, 3; Merced Lake, 7,500 ft., 2; Mono Meadow, 7,300 ft., 1; Chinquapin, 6,200 ft., 1; El Portal, 2,000 ft., 2; Coulterville, 2; Pleasant Valley, 1. Merced County: Snelling, 1; Los Baños, 1. Madera County: Raymond, 2. Fresno County: Mendota, 4; Panoche Creek, at 502 ft., 1; Friant, 1; Kings River, 5,000 ft., 2. Ventura County: Matilija, 4; Ventura, 3. Los Angeles County: vicinity of Pasadena, 7; near Azusa, 2. San Bernardino County: near Colton, 4. Riverside County: Thomas Mountain, 6,800 ft., 1. San Diego County: Warner Pass, 3; Grapevine Spring, 1; Witch Creek, 8; Julian, 8; Cuyamaca Mountains, 4; San Diego, 2; Point Loma, 10; Chula Vista, 3; near mouth Tiajuana River, 1; Dulzura, 7; Campo, 1; Jacumba, 1; Mountain Spring, 4.