84 University of California Publications in Zoology [Vol. 12 



holes, was 60 inches in eircumference of trunk two feet above the 

 ground, first branch four feet above the ground, and total height 24 

 feet. 



It i.s thus apparent that birds of arboreal habit find only in the 

 wash association of the desert a near approach to conditions preferred 

 elsewhere, and this doubtless accounts for the conspicuous transient 

 arboreal element occurring in this association. But the greatly reduced 

 foliage, giving most of the above-named trees the aspect of winter 

 leaflessness. results in close resemblance to finish or shrubbery, as 

 indicated by the prevalence of the brush-inhabiting category of breed- 

 ing birds affecting them. 



The iron wood occasionally harbors clumps of mistletoe (Phoraden- 

 dron californicum) in common with the mesqiiite of the riparian belt. 

 This accounts for the presence of certain berry-eaters. There are also 

 berry-producing shrubs bordering the washes, notably Lycium ander- 

 soni and Lycium parishi. The former occurs widely as a character- 

 istic member of the catclaw association. The latter, a much larger 

 thicket-forming shrub, was noted only in small washes in the vicinity 

 of Picacho. As already noted. Atriple.r polycarpa occurs in an exten- 

 sion of the -saltbush association leading tip along each side of nearly 

 all of the larger washes. 



Bird-life is better represented in the catclaw association than in 

 any other of the desert associations. Some of the species are closely 

 adherent to it, being evidently by structure and habits dependent 

 upon the conditions pertaining to thorny brush. But mammals are 

 relatively less numerous. Only one rodent finds its maximum abund- 

 ance along the washes {Perognathus penicillatus penicillatus, see fig. 

 D), and it is possible that even of this species, the metropolis is in 

 the adjacent sandy saltbush tract, and that trapping really waylaid 

 the individuals foraging at large away from their homing places. 

 Times of deluge, even if of rare occurrence, are doubtless accompanied 

 by great mortality of ground-dwelling mammals along these washes. 

 This factor must be one of no small import in determining the biotic 

 constitution on the several levels of the desert surface. 



