MAJOR PLANTS _Bromus sp._ _Artemisia tridentata_ _Chrysothamnus nauseosus_ _Purshia glandulosa_ This association is found on only the crest and desert slope of the range between 5000 and 8000 feet elevation. There it characteristically occupies flats and clearings in the yellow pine forest and pinyon-juniper woodland. The dominant plant of the association is basin sagebrush, and in many places this plant forms mixed growths with snowbrush and _Haplopappus_. The low brush of this association is formed by closely spaced bushes with grasses growing between. Because of its limited occurrence in the San Gabriel Mountains, this association there has relatively little effect on mammalian distribution. Locally, nevertheless, the presence of this association governs the distribution of certain mammals. For example, on Blue Ridge, islands of sagebrush amid the conifers provide suitable habitat for _Dipodomys agilis perplexus_ and _Perognathus californicus bernardinus_; and in Swarthout Valley _D. a. perplexus_, _Reithrodontomys megalotis longicaudus_, and _Lepus californicus deserticola_ are seemingly restricted to the sagebrush flats. Joshua Tree Woodland Association MAJOR PLANTS _Yucca brevifolia_ _Lycium Andersonii_ _Eriogonum fasciculatum_ _Tetradymia spinosa_ _Ephedra sp._ _Larrea divaricata_ This association is on the piedmont that dips toward the Mojave Desert from the interior base of the San Gabriels. The widely spaced Joshua trees with low bushes between, and the dry washes breaking the level terrain below the mouths of canyons are typical of this area. Field work was extended no farther down into the desert than about the 3500 foot level, where this association was still dominant. 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.