70 



University of California Publications in Zoology [Vol.12 



Icteria virens longicauda: excl.; sum- 

 mer 



Wilsonia pusilla pileolata: max.; 

 transient 



Wilsonia pusilla chryseola: min.; 

 transient 



Troglodytes aedon parkmani: excl.; 

 winter 



Regulus calendula cineraeeus: excl.; 

 winter 



Polioptila caerulea obscura: min.; 



winter 

 Hylocichla ustulata ustulata: excl.; 



transient 

 Hylocichla guttata guttata: excl.; 



winter 

 Planesticus migratorius propinquus: 



max.; winter 



Odocoileus hemionus eremicus: min. 



(?) 

 Peromyscus maniculatus sonoriensis: 



max. 

 Sigmodon hispidus eremicus: max. 

 Reithrodontomys megalotis deserti: 



min. 

 Sylvilagus auduboni arizonae: min. 

 Felis oregonensis browni: max. 



Urocyon cinereoargenteus scotti: max. 

 (foraged in all other riparian as- 

 sociations) 



Mephitis estor: min. 



Procyon pallidus: min. 



Antrozous pallidus pallidus: max. 

 (?) 



Myotis oecultus: max. (?) 



Nyctinomus mexicanus: max. (?) 



Remarks upon the Willow-Cottonwood Association. — The predom- 

 inating plants in this association were : willows of at least two species 

 {Salix nigra and Salix fluviatilis), the Cottonwood (Populus fremonti), 

 and guatemote (Baccharis ghdinosa). The latter occurred chiefly as 

 an undergrowth where the willows or cottonwoods had reached large 

 size. Practically all of the area occupied by this association is subject 

 to inundation annually in early summer, of from a few inches to as 

 much as twelve feet. Only such plants as can survive this period of 

 drowning are able to occupy the flood-bottom of the river. 



Furthermore, as explained in the general description of the river 

 (p. 59), much of the overflow bottom is subject to destructive erosion 

 through continual changing of the river's channel. By this process 

 all vegetation in its path is swept away at frequent intervals. Only 

 such trees as are of rapid growth are able to maintain a representation 

 on the major part of the bottom lands. 



No plants of the willow-cottonwood association (or it may be more 

 briefly referred to as simply the willow association) occurred also on 

 the upland deserts, and conversely no true desert plant occurred in 

 the overflow area. Only one possible exception was observed, the 

 serewbean (Prosopis pubescens) which occurred in mixture with wil- 

 lows in a few places, where the flood-bottom was old, that is, had not 



