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Geophysical
Attributes
DeKalb County, Illinois
SIZE
DeKalb County is a parallelogram of rich soil, about 36 miles
long and 18 miles wide (58 km x 29 km). It covers an area of
636 square miles comprising 407,040 acres (164,725 hectares). |
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GLACIATION
During the "Great Ice Age" snow and ice radiated out of Canada and
dislodged and transported large quantities of rock and related material
great distances. When this ice melted, the glacial material or till
was deposited creating an underlaying ridge or moraine. The outwash
from this melt created much of the flatland in the county. The depth
of glacial material over DeKalb County varies from 40 to 450 feet
(12 to 137 m). Over this glacial material is a loess (windblown)
deposit that averages about 18 inches (45 cm). Where little or no
erosion has taken place, this loess deposit makes a "gardenlike"
soil with no rocks or boulders on top.
SLOPE, DRAINAGE, AND SOILS
Most of DeKalb County ranges in elevation between 700 and 950 feet
(213-290 m) above sea level. 58 percent of the land area has a slope
of 0-2 percent. 41 percent is in the 2-7 percent slope range. The
soil is permeable and in most cases is readily drained by tile and
ditches. Drummer silty clay loam is an important black soil type
with the surface 12 to 20 inches (30-51 cm) thick. The subsoil is
18 to 24 inches thick (45-61 cm). About 98 percent of DeKalb county
is considered prime farmland by Natural Resources Conservation Service
criteria.
CLIMATE
The -26 degrees F (-32 degrees C) in 1933 represents one of
the lowest temperatures ever recorded and one of the highest
temperatures was 109 degrees F (43 degrees C) in 1936. The average
date of the last killing frost |
| has been May 4 and the average date
of the first killing frost in the fall was on October 7. The
growing season averages approximately 157 days. Rainfall averages
35 inches (90 cm). Prevailing winds are from west and southwest.
Snow averages 36 inches (91 cm) annually. |
| LAND USE |
| DeKalb County is predominately agricultural and land is used
as follows: |
| Cropland |
88% |
| Forest and Woodland |
1% |
| Grazing |
1 % |
| Cultural Development |
14% |
| Over 97 percent of the land in the county is in capability
classes I and II. |
MINERALS
DeKalb County is not rich in minerals. Limestone, dolomite, sand,
and gravel are the chief minerals in the county.
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