i9iq] VESTAL— PHYTOGEOGRA PHY OF COLORADO 155 



vegetation of the detrital outwash from the hills is succeeded by 

 the line soil and mostly short-grass vegetation of the shale beds 

 covering most of the Great Plains surface. 



Plaji of presentation. — The writer has been much influenced by 

 the work of Davis (i) on the geography of the Colorado Front 

 Range, a regional presentation and particularly relevant in this 

 study, since the area considered is so nearly the same. Davis' 

 systematic treatment avoids repeating descriptions of frequently 

 encountered land-forms by recognizing their common features and 

 giving each a brief characterization and a name, thus identifying 

 them when mentioned later. Minor differences of detail are not 

 considered in the condensed treatment thereby made possible. 

 In a regional study, in which numerous elements form an intricate 

 complex, this omission of detail is essential. As the physical 

 geographer refers land-forms to types (mental counterparts of 

 physical realities), so in a regional study of plant geography one 

 may refer forms of vegetation to types which are the same over 

 considerable areas. This is a common practice in ecological 

 classification, but many studies of limited areas of vegetation have 

 characterized the plant communities without regard to geographic 

 orientation. If possible, local representations or variants of wide- 

 spread associations should be recognized as such. The characteri- 

 zation of the relatively few widespread and important vegetation- 

 types makes it possible to systematize plant geography. This 

 systematic treatment emphasizes the common features, the resem- 

 blances of similar plant communities, but the differences, when 

 worthy of note, can always be stated in addition. The section of 

 this study which is here published is the systematic part, which 

 establishes the types of topography, soil, climate, and vegetation as 

 developed in the region or in parts of it. It will be followed by a 

 regional section, which describes the physical and vegetational 

 features "in their actual spatial relations," to use the words of 

 Davis, and by parts deahng with general geographic and develop- 

 mental relations of the vegetation. 



Physical features 



The area studied is the eastern front of the Rocky Mountains 

 in Colorado, of which the most characteristic part is the Front 



