4 University of Michigan 



Prairies. This marks the eastern boundary of the Drift Prairie 

 Plain, which has a general elevation of from 1,500 to 1,800 

 feet, rising gradually toward the west. It is bounded in that 

 direction by an abrupt escarpment 600 to 700 feet high, mark- 

 ing, the eastern boundary of the Great Plains, and known as 

 the Cotean du Missouri; this runs from near the northwest 

 corner of the state in a general southeasterly direction to the 

 southern border. Within the boundaries of the broader por- 

 tion of the Drift Prairie Plain are two minor physiographic 

 features, the Mouse River Valley and the Turtle Mountains, 

 which depart somewhat from the general character of this 

 region. That entire portion of the state, constituting approx- 

 imately half of its area, which lies to the southwest of the 

 C&teau dti Missouri is occupied by the Missouri Plateau sec- 

 tion of the Great Plains province. Its surface varies from 

 1,800 to considerably more than 2,700 feet elevation, increas- 

 ing in height toward the southwest. Subordinate but striking 

 topographic features are the valleys of the Missouri River 

 and its tributaries, and the "Little Bad Lands" of the Little 

 Missouri River near the western edge of the state. 



The humidity decreases as one goes from east to west across 

 the state; the Red River Valley is comparatively moist, the 

 Drift Prairie Plain semi-arid, and the Great Plains section 

 an arid, semi-desert steppe. The vegetation corresponds rather 

 closely to this change in humidity ; in the eastern part of the 

 state the streams and lakes are bordered by heavy forest, and 

 the prairie is covered with a fairly thick and sometimes tall 

 growth of grasses and other herbaceous plants ; as one pro- 

 ceeds westward the trees rapidly disappear, the vegetation 

 becomes scantier and more stunted, and the characteristic 

 plants of semi-desert regions, such as sage-brush and cacti, 

 become more numerous. These changes are gradual, corre- 



