1914] 



VES TA L—PRA IRIE V EG ETA TION 



379 



mesas 



which have been described by Lee (ii) and which are discussed 

 also by Fenneman (4) and by Dodds (3). The physiographic 



(fig. 1); they are as 



map 



follows : 



■ 



i. The foothills, with their hogback ridges and upturned crags, locally 

 quite variable in soil, exposure, slope, etc. 

















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L^" 



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, 



K 





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Fig. 2. — Green Mountain and its mesas: in the foreground the mesa- terrace level 

 occupied by a modified short-grass growth; next the floodplain of South Boulder 

 Creek; next a continuation of the mesa-terrace; above that the higher mesa level, 

 interrupted, with long slopes, and graded tops partly covered with pines; October 191 3. 



2. The mesas of the older and higher level, not continuous along the 

 mountain-front. 



3. The mesa-terrace, a more extensive, lower, and more recently graded 

 surface. 



4- The floodplain, of the present and still lower stream grade, generally 

 debris-covered as the two mesa levels. 



5. The plains proper, usually separated from the mountain-front, and with 

 generally fine soil, residual or aeolian. 



The first four divisions may be distinguished in fig. 2. 

 A mesa may abut at its head upon the higher slopes of the foot- 

 hills or of a mesa of a higher level, or it may be isolated, cut off by 



