THE WORK OF STREAMS 



167 



tains may develop. In the western part of the United States 

 such an elevation of moderate height and extent is often called 

 a mesa (a Spanish word 

 meaning table, prono\mced 

 "may-sa"; Figs. 169 and 

 170). Smaller mesas whose 

 flat tops have been de- 

 stroyed more or less com- 

 pletely by erosion are fre- 

 quently called buttes (a 

 French word meaning hill, 

 pronounced "bewts"; 

 Fig. 171). The name butte 

 is sometimes applied 

 loosely in the West to any 

 conspicuous hill. 



Rock structure and 

 stream courses. Joint 



FIG. 168. A hogback. East flank of 

 Bighorn Mountains, Wyoming. (Trow- 

 bridge.) 



systems and fissures have in certain places guided the run- 

 off (Fig. 172), producing 

 drainage systems of peculiar 

 and angular pattern. Many 

 streams in the Adirondack 

 Mountains flow along inter- 

 secting fault lines. In a re- 

 gion underlain by horizontal 



FIG. 169. Mesas. Eastern Ari- 

 zona. (Fairbanks.) 



beds, lengthening valleys extend 

 themselves in various directions, 

 and the stream courses are with- 

 out systematic arrangement 

 (Plate IV). In an area of tilted 

 beds of unequal strength, many 

 of the larger streams follow the 



FIG. 170. Mesa Pino, New 

 Mexico. 



