1!,14 l Grinnell: Mammals and Birds of the Colorado Valley 59 



Ehrenberg, Palo Verde and Cibola are located in it, and considerable 

 activity lias of late been directed towards farming the rich bottom 

 lands. But the capricionsness of the river has proven a hindrance 

 tn marked development along this line. 



Shortly below the point where the river emerges from its rock-con- 

 fined channel into the broadening valley, meandering begins. The 

 detours of the stream increase in extent towards the lower end of the 

 valley, the channel swinging from side to side in great curves, marked 

 by minor curves alone- these courses, so that a sort of periodicity of 

 meandering is exhibited. The most notable phenomenon in this con- 

 nection is the progressive movement of these loops down the valley. 

 The result is that in a short period of years, the major portion of 

 the river's flood-bottom is worked over in the path of this irresistible 

 and continual shifting of the channel. 



The effect on the flora is obvious. Only in curves of the valley 

 sheltered by abutting hills are trees given a chance to reach advanced 

 age. The only trees capable of thriving on the unstable portion of 

 the flood-bottom are such as grow rapidly, willows and cottonwood. 

 As the observer floats along the main channel, winding through the 

 great valley, especially during rising water, the destructive process 

 in question is clearly in evidence. On the outside of each curve the 

 river rapidly undercuts the bank, dislodging great masses of the fine 

 sedimentary soil, itself laid down but a few years previously. The 

 overgrowth of comparatively aged willow and cottonwood topples 

 into the stream and is swept away by the swift current. Hundreds 

 of acres may be thus appropriated by the river in a few days and 

 within a short distance. 



On the other hand, on the inside of each curve, where the current 

 is slow, and especially during falling stages of the water, the river is 

 rapidly depositing sediment, in other words building up its bank 

 towards the general level of the bottom lands. At the annually 

 recurring periods of high water, when the entire flood bottom is 

 inundated, layers of silt are deposited over the whole, thus tending 

 to establish a uniform level. 



The observer, from any appropriate hill-top overlooking the valley. 

 can readily discern the regularly graded heights of tree growth which 

 mark the successive ages of the land on which they grow. The year- 

 old seedlings but a few T inches in height form a crescent-shaped belt 

 along the inside of each curve of the river, facing down the valley. 

 Paralleling this and next in position back from the river is dense 



