170 PUBLIC PARKS OF IOWA 



wind in and out among the hills of drift. Indeed, the first definitely 

 marked water course in this direction is found near Thornton in the 

 eastern part of Grimes township. 



The area of the Altamont moraine is one of unique topography. 

 Geographically it corresponds very nearly with the western tier of town- 

 ships so far as it is included in Cerro Gordo county. In the southwest it 

 extends a short distance east of the limit of these, and occupies a few 

 square miles in the western edge of Mount Vernon and Pleasant Valley 

 townships. The surface of the area is quite irregular and presents a 

 series of knob-like hills and undrained marshes arranged in the most 

 lawless manner. Erosion has played a very unimportant part in pro- 

 ducing the present surface configuration of this morainic belt. 



One of the most broken and hilly portions of the moraine in Cerro 

 Gordo county occurs in the northwest corner of Grant township. The 

 hills are simply knobs of drift that were irregularly heaped up along the 

 margin of the Wisconsin ice. Their height above the tortuous, marshy 

 valleys that wind in and out and branch and rebranch without definable 

 system, so as practically to surround each individual knob, varies from 

 forty to seventy or eighty feet. The slopes are often steep. The traveler 

 following the wagon roads must be content to make slow progress and 

 must often make long detours to avoid impassable marshes or impractica- 

 ble hills. 



The topography of the greater part of Cerro Gordo county might be 

 regarded by some observers as somewhat characterless and monotonous. 

 Leaving out the western tier of townships the remaining portion of the 

 county is a gently undulating drift plain, almost level over large areas. 

 Stream valleys that have cut to but a very limited extent below the gen- 

 eral level, and a few knobs or ridges that rise to a height of twenty to 

 thirty feet above the otherwise unbroken plain, give some diversity to a 

 landscape in general devoid of salient topographical features. The drift 

 covering the county is in some places very thin; erosion since the deposi- 

 tion of the drift has been insignificant in amount, and hence the most 

 conspicuous hills and valleys of eastern Cerro Gordo are in reality rem- 

 nants of preglacial topography. 



All the eastern part of the county is occupied by lowan drift; the 

 western tier of townships is almost wholly occupied by the knobs, ridges 

 and kettle holes that characterize the marginal moraine of the Wisconsin 

 drift, the Altamont moraine of Chamberlin. A small area in the south- 

 west corner of Grimes township presents some of the characteristics of 

 plains of Wisconsin drift, but this last area is so small as to make it com- 

 paratively unimportant. The county is, therefore, topographically divisi- 

 ble into two principal areas, the area of the lowan drift and the area 

 of the Altamont moraine. Iowa Geological Survey, Vol. VII, pp 136-9, 142 

 and 132-3. 



