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Til 
GENERAL FEATURES OF REGION 
Johnson County, Iowa, may be located geographically by its 
county seat, Iowa City, which has a latitude of 41° 40’ and a 
longitude of 91° 31’ 30”. In United States land surveys, John- 
son County is included in townships 77-81 north and ranges 
5-8 west of the principal meridian. It contains approximately 
618 square miles in extent and consists of a square of 24 by 24 
miles, to which is appended an additional township on the south- 
east corner. This southeast township, Fremont, is six miles in 
its north and south dimensions and averages seven miles in 
width east and west. Its east boundary is continuous with the 
east boundary of the rest of the county, and its west edge is 
bounded by the southward wanderings of the Iowa River. 
GEOLOGY 
As Calvin pointed out,* except for certain local outcroppings 
of rock of the various strata of the Paleozoic age, the surface 
formations of Johnson County had their origins in the Glacial 
and Postglacial epochs. These outcroppings are, with rare ex- 
ceptions, bluffs adjacent to the Iowa River and certain of its 
tributaries, more especially to those entering it from the north 
and east. 
The remainder of the surface has been formed of the glacial 
drifts of the Kansas and Iowa ice sheets, which in turn have 
been overlain with loess except for a naked lobe of Iowa drift 
extending a few miles into the county from the northwest. 
Through and upon these, the larger streams have established 
their fiood plains, which in the upper and lower parts of the 
county are of considerable width. Plate I is an adaptation of 
Calvin’s map of the surface deposits, modified to show only the 
surface or soil areas. The hatched areas indicate the naked 
lobes of the Iowa drift; the stippling represents alluvium de- 
posit, and the plain sections indicate the deposits of loess upon 
underlying glacial drift. 
Johnson County is peculiar in that the highland lies for the 
*Calvin, ‘Geology of Johnson County,’ Annual Report of Iowa Geological Survey, 
VII (1897), pp. 33-116. 
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