Little Colorado Valley, Arizona, 493 



Vegetation on the lowlands bordering the Little Colorado 

 consists of scattered chimps of grass set in the midst of yucca 

 and cactus "and interspersed with lone pinons and struggling 

 cedars of small size. Along the river a few cottonwoods and 

 willows furnish welcome shade. On the Coconino Plateau the 

 wide, open valleys and the broad, flat divides are mantled 

 with grass and support a forest of yellow pines, pinon and 

 cedars. 



The soil of the lowlands is, in many places, absent ; where 

 present it forms a thin coating for bed rock and its fine ingre- 

 dients are continuously removed by sudden downpours and by 

 the wind. 



The few Navajos who inhabit this region maintain a precari- 

 ous existence as nomads and range widely with their flocks in 

 search of forage and water. The area is distinctly unfavorable 

 for agriculture even in its most primitive form, and the 

 absence of ancient ruins indicates that it has long remained 

 unsuited to the needs of sedentary cliff-dwellers and their 

 descendants, the Hopis. 



Physiography. 



The primary features of this area are structural. The surface 

 of the Coconino Plateau is developed in harmony with lime- 

 stone strata which vary little from horizontality. The steep 

 east face of the plateau is the stream-gashed limb of a mono- 

 cline ; the slopes leading to the river are the dip slopes of sedi- 

 mentary beds. The master stream of the region, the Little 

 Colorado, throughout its course in the area under discussion, 

 has developed along the strike of the tilted beds and has 

 cut its way downward in the effort to maintain an accordant 

 junction with the Colorado. In the shales and weak sandstones 

 of the Upper Triassic, the river has opened a wide valley ; in the 

 Shinarump conglomerate and especially in the resistant Kaibab 

 limestone, narrow canyons are normal features. The tributaries 

 of the Little Colorado are consequents whose direction is slightly 

 modified by jointing. The prevailingly flat interstream spaces 

 are dissected by tiny canyons and carry on their surface many 

 small mesas and buttes of rock of younger age, which are 

 frequently eroded by water and wind into fantastic forms. 



In physiographic development the Tanner's Crossing area 

 has experienced the episodes which mark the history of the 

 Plateau Province as a whole. Following a period of mono- 

 clinal folding, whose record may be read in Coconino Point, 

 Black Point, and in the gentle fold located midway between 

 the east face of the Coconino Plateau and the Little Colorado, 

 the region was reduced to a plain of low relief. Remnants of 



