NumberPer cent
of total
Perognathus fallax pallidus311.5
Dipodomys agilis fuscus934.6
Peromyscus truei montipinoris1038.5
Neotoma fuscipes simplex415.4

Although Munz and Keck (1949:101) considered the pinyon-juniper belt as one association, on the desert slope of the San Gabriels pinyons and junipers do not generally grow on common ground; but rather the juniper belt represents a well defined habitat occurring between the pinyon covered slopes and the flats that support Joshua trees. Because the mammalian populations of the pinyon belt and the juniper belt are somewhat different, the mammals of these areas are most conveniently taken up separately.

In the juniper belt the juniper tree is of marked ecologic significance; the distribution of Peromyscus truei and Neotoma fuscipes is determined here by the presence of junipers. At certain times of year the fruit of this plant is eaten by coyotes, kangaroo rats, and wood rats.

The list below indicates the results of approximately 500 trap nights in the juniper belt near Mescal Canyon, between 4000 and 5000 feet elevation.

Table 7.—Yield of 500 Trap-nights in the Juniper Belt.

NumberPer cent
of total
Perognathus fallax pallidus1616.7
Dipodomys merriami merriami33.1
Dipodomys panamintinus mohavensis3637.5
Peromyscus truei montipinoris2222.9
Peromyscus maniculatus sonoriensis1212.5
Neotoma lepida lepida22.1
Neotoma fuscipes simplex22.1
Onychomys torridus pulcher33.1

The biota of the washes that cut through the juniper belt in and below many of the larger canyons differs from that of the surrounding juniper-clad benches. Because the washes are in the same geographic area as the juniper belt they are discussed together. These washes on desert slopes are densely populated by rodents derived from adjacent areas, and support vegetation typical of higher floral belts in association with xerophytic, typically desert, species. In a sense, the washes serve to mix up the mammals of adjacent areas. For example, Onychomys torridus pulcher and Peromyscus eremicus eremicus, which are mammals typical of the desert, were found in Mescal Wash above their usual desert range; and Peromyscus californicus insignis and Peromyscus boylii rowleyi, which are chaparral inhabiting mammals, were found in the wash far removed from their chaparral environment. Washes are evidently effective agents in facilitating the dispersal of certain species of mammals. It is easy to envision a species crossing hostile habitats via dry washes to invade suitable niches in an area which is geographically and ecologically isolated from the original home of the species. Approximately 500 trap nights in Mescal Wash, at 4100 feet elevation, in the lower edge of the juniper belt, yielded the following mammals:

Table 8.—Yield of 500 Trap-nights in Mescal Wash (Desert Slope).

NumberPer cent
of total
Perognathus fallax pallidus54.5
Dipodomys panamintinus mohavensis4338.7
Peromyscus californicus insignis32.7
Peromyscus truei montipinoris1.9
Peromyscus boylii rowleyi21.8
Peromyscus eremicus eremicus2825.0
Peromyscus maniculatus sonoriensis2320.5
Onychomys torridus pulcher43.5
Neotoma lepida lepida32.7

Dipodomys panamintinus mohavensis, Neotoma fuscipes simplex, and Peromyscus truei montipinoris are probably the most characteristic mammals of the pinyon-juniper association.