EROSION AL HISTORY OF DRIFTLESS AREA 63 



at Monona, Luana and Watson in the southeastern part of 

 the Waukon quadrangle, at National, Garnovillo, Upde- 

 Graff, Colesburg, an area east of Graham, Luxemburg and 

 other points in the Elkader quadrangle, and at or near 

 Holy Cross, Sherrill, Rickardsville, Bankston, Balltown, 

 and Tivoli in the Iowa portion of the Lancaster quadrangle. 

 In the extreme southern part of the Driftless Area in the 

 Iowa portion of the Galena quadrangle there are consider- 

 able areas of flat land on high divides, which are used for 

 upland farms and roads. 



Flat summit areas with accordant levels are not extensive 

 in Minnesota. They are best developed in the western parts 

 of Winona and Houston counties. In Winona county a 

 strikingly flat plain of about 15 square miles in area lies 

 between Utica and St. Charles and to the south from there. 

 It is approximately 1300 feet above sea level. Near Spring 

 Grove, Houston county, at an elevation of approximately 

 1325 feet, the summit plain is represented by extensive 

 prairie-like uplands, spurs of which ramify from the main 

 area. Similar conditions occur also in the neighborhood of 

 Caledonia. 



From the foregoing descriptions, the significant facts 

 concerning the topography of the summit surfaces in the 

 Driftless Area may be summarized as follows: (1) There 

 are many divides whose summits are noticeably even. (2) 

 Some of these areas of upland flat are long and broad. (3) 

 The various areas of upland flat have such slight irregular- 

 ity in comparison with the rest of the topography that they 

 are favorable sites for farming. (4) If the elevations of 

 isolated summit areas in a given district be compared, they 

 are found to be strikingly accordant, though not identical. 

 (5) Accordant summit levels are known in practically all 

 portions of the Driftless Area. (6) The districts where 

 the summit plains occur are close enough together to war- 

 rant correlation from one district to another; from Bara- 

 boo, through the Richland Center and Mineral Point quad- 

 rangles to Jo Daviess County, Illinois; from Baraboo to 

 Sparta ; from Sparta through Viroqua and Prairie du Chien 

 to Iowa; from Dodgeville via Bradtville to National, Iowa; 



