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294 University of California Publications in Zoology IT OL - 16 



The dependence of animals on their habitats does not seem to have 

 been sufficiently taken into account in the study of distribution. Many 

 species are closely restricted to certain kinds of habitats. If a particu- 

 lar kind of habitat does not occur in a region the species of animals 

 restricted to it must also be absent. This applies to the habitats of 

 great extent as well as to the habitats which always occur in limited 

 areas. We should not expect to find typically desert animals except 

 in a desert habitat. In order to explain distribution we should give 

 much attention to the causes producing the different kinds of habitats. 



Usually the fauna of each geographical region has been studied as 

 a whole and whole faunas have been compared together without regard 

 to differences in the habitats of the component species. It seems that 

 such a method cannot lead to the most exact knowledge of the factors 

 limiting the distribution of animals on the continent of North America 

 or of the relation in origin of particular species or faunas. 



In order to show the relation of the faunal areas of southeastern 

 Washington to the faunal divisions of North America, the position of 

 the region in the zoogeographical system of considering distribution 

 and in the life-zone system is determined as closely as possible. Finally, 

 a critical comparison is made of the several methods of studying animal 

 distribution which are at present in use. 



The latter part of the field-work and the preparation of the results 

 have been supervised by Professor S. J. Holmes, who has given much 

 valuable criticism. I am also indebted to Dr. Joseph Grinnell for 

 advice and criticism. Professor J. C. Merriam furnished most of the 

 notes on the geological history of the region. 



TOPOGRAPHY 



The topographical features of southeastern Washington have been 

 described in detail by Russell (1897, pp. 14-28). The western part of 

 Walla Walla County has in general a low relief and is largely formed 

 of several "Flats." However, south of the Walla Walla River in this 

 region there is a high range of hills. 



East of Lamar the hills become somewhat abruptly higher and the 

 prairie region of eastern Walla Walla County and western Columbia 

 County is characterized by high, rolling hills. The hills are steepest on 

 the northeast slopes and these northern hillsides are damper and colder 

 and support a more luxuriant growth of vegetation than the southern 

 slopes. Along the northern boundary of Walla Walla and Columbia 



