PLATE 6 



Kg. 6. Portions of quail-brush (in foreground) and mesquite associations, 

 paralleling each other and situated next outwardly from the arrow-weed asso- 

 ciation. Photograph taken on the Arizona side about one mile above Mellen, 

 February 27, 1910. On this date the deciduous mesquites were still leafless, the 

 dark patches being masses of the mistletoe (Phoradendron calif ornicum) . The 

 latter parasitic plant produces an almost perennial and abundant crop of 

 berries which form a staple food supply for many species of birds, notably 

 the phainopepla, western bluebird, western robin, and mockingbird. The 

 quail-brush (Atriplex lentiformis), because of its stoutly interlacing and spiny 

 branches, forms an ideal refuge for such animals as the cottontail rabbit and 

 desert quail. Abert towhees are permanent inhabitants of this belt as well 

 as of the adjacent one on each side, while the winter-visiting Zonotrichias 

 make it their headquarters. 



Fig. 7. Mesquite (Prosopis juliflora) in full leaf and fruit, the latter the 

 bean-like pods. The mesquite marks a distinct association, the outermost one 

 of the riparian set of associations. Both the foliage and the fruit constitute 

 important food sources for many of the animals of the region, either directly 

 or indirectly. Among birds, characteristic permanent residents are the crissal 

 thrasher and Abert towhee. The Colorado river wood rat (Neotoma albigula 

 venusta) is a characteristic mammal. Photograph taken near Pilot Knob, May 

 11, 1910. 



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