PREGLACIAL MOINGONA RIVER 



55:; 



magnitude of the Pre-Glaeial river work and to a position of 

 this region at a higher level in late Tertiary times. 



The relative magnitude of the present Des Moines river and 

 of the Old Moingona river are best displayed perhaps in the 

 city of Des Moines. The present used gorge is scarcely more 

 than half a mile wide and for a part of the way is not more 

 than a quarter of a mile in width, with a firm rock-bottom, (figure 

 175). The ancient abandoned gorge is more than two miles wide 

 and its bottom is 100 feet beneath the low-water level in the 

 river of today. 



_»gaii>Mis«aaa a i.i>iiii > nt rtw i'-^ - 



Fig. 175a. — Cantonment of Camp Dodge on Beaver Valley floor, in ancient 

 gorge of old Moingona river. (Piioto by Lees.) 



Something of a true insight into the character of Iowa's Pre- 

 (ilacial drainage is obtained from consideration of the present 

 waterways outside of the drift-mantled area. In Tertiary times 

 the lowest line of the central depression was no doubt occupied 

 by a master-stream much in the same position that it is today. 

 By the rising of the Rocky Mountains the rivers from the west 

 must have been directed eastward down the gentle slope until 

 tliey reached the Old Mississippi. Their ending with the Missouri 

 river is a later or G-lacial consequence. At any rate several of 

 them must have continued directly across Iowa and Missouri. 

 With the advance of the continental ice sheet the northern rivers 

 including the Yellowstone and the Upper Missouri which had 

 long flowed into Hudson Bay must have been blocked in their 

 northern reaches and diverted southward. By the time the ice 



