Although the vegetation of this area is scattered and sparse, presenting a barren and sterile aspect, the area supports a rather high population of rodents. The soil at the bases of many large box-thorn- and creosote-bushes is perforated by burrow systems of Dipodomys panamintinus or Dipodomys merriami, and those burrows abandoned by kangaroo rats are used as retreats by Onychomys torridus and Peromyscus maniculatus. The mammals of this association are all characteristic of the fauna of the Mojave Desert, with the ranges of such species as the coyote and jack rabbit extending well up the desert slope of the mountains.
The mammals listed below were taken in 1948 in roughly 400 trap nights in the Joshua belt, at an elevation of 3500 feet, one mile below the mouth of Graham Canyon.
Table 9.—Yield of 400 Trap-nights in the Joshua Tree Belt.
| Number | Per cent of total | |
|---|---|---|
| Dipodomys panamintinus mohavensis | 36 | 59.0 |
| Dipodomys merriami merriami | 15 | 24.6 |
| Onychomys torridus pulcher | 4 | 6.6 |
| Peromyscus maniculatus gambeli | 6 | 9.8 |
Populations of Dipodomys merriami and D. panamintinus fluctuate widely, possibly in response to weather cycles. In November of 1948 trapping in the Joshua belt showed that panamintinus outnumbered merriami approximately three to one, whereas in December of 1951, after a succession of unusually dry years, merriami was the more numerous. Further, merriami occurred in the lower parts of the juniper belt in 1951 where in 1948 it seemed to be absent.
Dipodomys merriami merriami and Onychomys torridus pulcher are diagnostic of the Joshua tree woodland association in the San Gabriel Mountains area, since few individuals of either species occur outside of this association.
PLATE 1
Fig. 1. View of typical coastal sage scrub association, showing in foreground white sage, and coastal sagebrush. The adobe banks beyond are grown mainly to white sage. Small mammals are abundant in this association, with Dipodomys agilis, Perognathus fallax, and Sylvilagus audubonii being characteristic of the area. Photo March 25, 1952, at mouth of San Antonio Canyon, 1800 feet elevation.
