BLUE EARTH COUNTY. 417 



Topography. Eroded valleys.] 



river and its tributaries have cut channels that increase in depth from 50 

 to 100 feet along the upper portion to 150 and 200 feet near the Minnesota 

 valley. 



The central and southern portions of the county, embracing about three-quarters of its 

 whole area, are a level, or only slightly undulating sheet of glacial drift, except that the rivers 

 have cut deep valleys, which may be properly called channels, in the otherwise unbroken plain. 

 This expanse includes the following townships in their order from' the southeast: Danville, 

 Medo, McPherson; Mapleton, Beauford, Decoria, Mankato; Sterling, Lyra, Bapidan, South Bend; 

 Shelby. Vernon Center, Garden City; Pleasant Mound, Ceresco, and Lincoln. 



Exceptions to the prevailing flatness of this area are the rolling tract mentioned in the 

 northwest part of Sterling, reaching a mile or two north from the north end of lake Jackson, and 

 rising 30 to 40 feet above the general level; the northwest part of Lyra westward from Good 

 Thunder, and the most of Vernon Center and Garden City townships, undulating 10 to 20 feet in 

 long slopes; and section 25, Pleasant Mound, where a group of katnes. which suggests the name 

 of the township, extends about a mile from north to south, with a width of one fourth to one third 

 of a mile, consisting of many mounds, knolls, and short ridges, from 30 to 75 feet high, of no very 

 notable parallelism in trend, but perhaps most frequently elongated from north to south. Their 

 material is gravel, containing pebbles up to six inches in diameter, irregularly interstratified with 

 sand. Boulders up to two or three feet in diameter occur rarely upon the surface of the mounds. 

 In the south part of this section the contour charges to a more smoothed, rolling surface, with 

 crests 20 to 30 feet high. The material here is the unmodified glacial drift or till, which also forms 

 all the surrounding land, in prolonged low undulations. No other gravel deposits were observed 

 in this vicinity. 



Butternut Valley, Cambria, and Judsou, including the part of Blue Earth county northwest 

 from Lake Crystal, are gently undulating till, with the highest portions 10 or 20 feet above the 

 lowest, the slopes occupying from one fourth of a mile to one mile. Isolated knolls of fine gravel 

 and sand, 5 to 15 feet above the general level, occur rarely in these townships. Like the group 

 of kames in Pleasant Mound, these accumulations of modified drift are believed to have been 

 formed by streams that descended from melting ice-fields. 



In the northeast part of this county, Mankato is nearly level from the top of the bluffs of the 

 Minnesota river at the east side of the city through five miles east to Eagle Lake. To the east 

 and north, nearly all of Le Ray, Jamestown, and the east part of Lime, are slightly or moderately 

 undulating, with crests 10 to 25 feet above the hollows or 20 to 40 feet above the numerous lakes. 

 Sections 19, 20, 29, and 30 of Le Ray are in massive swells 30 to 40 feet high. The northeast part 

 of Jamestown, and the vicinity of Marysburg, are quite smooth, only undulating 5 to 15 feet in 

 long distances. 



Eroded valleys. The most notable topographic features of this county are the trough-like 

 valleys that have been excavated by its rivers. The valley of the Blue Earth river through 

 Shelby and Vernon Center is from 75 to 100 feet deep; in Rapidan and South Bend, before joining 

 the Minnesota valley, its depth becomes 200 feet. Its exposures of rocks underlying the drift 

 begin in section 13, Garden City, and extend interruptedly to its mouth. The width of this 

 valley, between the tops of its bluffs, is mainly from a quarter to a half of a mile. 



Watonwan river, tributary to this from the west, has a valley 60 to 75 feet deep through 

 Ceresco, and from 100 to 150 feet deep through Garden City. Its only rock exposures are a few 

 low outcrops of Shakopee limestone. 



Maple river, tributary to the Le Sueur river, flows from south to north , being through the center 

 of the county nearly parallel with the Blue Earth river and three miles east from it. In Mapleton 

 and Sterling the valley of the Maple river is 40 feet below the general level; at Good Thunder, 75 

 feet; and near its mouth in Rapidan, 150 feet. The last two miles of this river, in sections 24, 13 

 and 12, Rapidan, have frequent exposures, and good quarries, of the Shakopee limestone. 



The Big Cobb river empties into the Le Sueur about one and a half miles farther east. Its 

 valley increases in depth fro"m 40 feet in the southeast part of the county, to 100 feet at the quar- 

 ries of Shakopee limestone in sections 19 and 18, Decoria, which are its only rock older than the 

 drift. The Little Cobb river in Medo flows about 40 feet below the general level, 



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