THE TEMPORARY MISSISSIPPI RIVER 423 



above sea level. A noteworthy feature of the northern Mud 

 Creek Valley is that the wide valley floor extends up into the tribu- 

 tary valleys so that the latter are exceptionally wide near their 

 mouths. "It is believed that these broad flood plains (of the tribu- 

 taries at their mouths) were filled from the main channel rather 

 than aggraded by their own creeks."^ The valley is not narrowed 

 at the divide. A short distance from the divide the Elkhorn Creek 

 Valley is divided by an island-like ridge into two branches, one 

 trending southwest and the other more directly south. The first, 

 which is the more conspicuous, has a direct course for more than 

 two miles and a width of half a mile. Its valley walls are well 

 developed and sharply outlined. The other branch, though wider, 

 is less well defined and is more circuitous. West of Durant, where 

 the branches reunite, the valley is well outlined for seven miles 

 and ranges in width from a mile and a half to a little over two miles. 

 It unites with the larger valley of Cedar River at Moscow. The 

 valley walls, although more sharply defined at some places than 

 others, merge gradually into the conspicuous feature of the valley, 

 a wide terrace. The surface of this terrace is fiat, and it is continu- 

 ous except where crossed by the narrow valley of Mud Creek, 30 

 to 45 feet below the terrace surface. 



Numerous exposures of sediment are found along the terrace 

 banks of the southern Mud Creek between Moscow and Durant. 

 The deposits seen in the various outcrops are of a uniform character. 

 In the eastern half of the valley the sediments consist of finely 

 laminated silts or clays, whereas in the western end of the valley 

 the deposits are made up of fine stratified sands. 



CEDAR RIVER VALLEY BETWEEN MOSCOW AND COLUMBUS JUNCTION 



Between Moscow, Muscatine County, on the north and Colum- 

 bus Junction, Louisa County, on the south is the unusually wide 

 valley of Cedar River (Fig. i). This valley is an extensive low- 

 land surrounded on all sides by drift uplands which rise above it 

 to the height of 80 to 100 feet. Its length is 24 miles and its 

 width 5|- miles. The valley is characterized by uninterrupted, 

 wide, and monotonously even terraces, the upper surfaces of which 



^W. H. Norton, "Geology of Scott County," Iowa Geol. Survey, Vol. IX (1899), 

 P- 415- 



