6 



NORTH AMERICAN FAUNA 73 



22" 



Fig. 2. Major physiographic regions of the St. Croix River Valley. 



major divisions by State and the reasons for the combining of systems that I 

 had to consider for interpretation. 



The most usable division system for Minnesota was developed by Kratz 

 and Jensen (1977). They developed a system based on both major vegeta- 

 tional and geomorphic provinces and included 17 distinct Ecological-Geo- 

 morphic divisions. Four of these divisions are included in the Minnesota 

 counties. A brief description of each follows. 



Southern Oak Barrens Section.— This section includes a large region of 

 southeastern Minnesota generally referred to as the Driftless Area, which 

 was not covered by ice during glacial periods. In the Valley, about 80% of 

 Washington County is included in this section. Topography is characterized 

 by highly dissected Umestone and sandstone hills adjacent to the St. Croix 

 River. Away from the river, large expanses of glacial outwash and kettle and 

 knob topography predominate. Vegetation consists of a transition between 



