[Illustration: FIG. 1. View of the juniper belt. This habitat forms the lower part of the pinyon-juniper association. _Perognathus fallax pallidus_, _Dipodomys panamintinus mohavensis_, and _Peromyscus truei montipinoris_ are typical of this area. Photo April 27, 1952, at Desert Springs, 4300 feet elevation.] [Illustration: FIG. 2. Joshua tree woodland association. The characteristic mammals are _Dipodomys panamintinus mohavensis_, _D. merriami merriami_, and _Onychomys torridus pulcher_. Photo January 4, 1952, 6 miles east and 2 miles south Llano, 3600 feet elevation.] 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). ========================================================== | Number | Per cent | | of total --------------------------------------+--------+---------- Perognathus fallax pallidus | 5 | 4.5 Dipodomys panamintinus mohavensis | 43 | 38.7 Peromyscus californicus insignis | 3 | 2.7 Peromyscus truei montipinoris | 1 | .9 Peromyscus boylii rowleyi | 2 | 1.8 Peromyscus eremicus eremicus | 28 | 25.0 Peromyscus maniculatus sonoriensis | 23 | 20.5 Onychomys torridus pulcher | 4 | 3.5 Neotoma lepida lepida | 3 | 2.7 --------------------------------------+--------+---------- _Dipodomys panamintinus mohavensis_, _Neotoma fuscipes simplex_, and _Peromyscus truei montipinoris_ are probably the most characteristic mammals of the pinyon-juniper association. Sagebrush Scrub Association