Till Plains Section of the Central Lowland Province of the Interior Plains.
The southern tip is in the Osage Plains Section of the same province and division.
Area entirely in Illinois.
Total Land Area 7,450 square miles (19,300 square kilometers).
The towns of Kewanee and Galesburg are in the western part of the area.
The towns of Macomb, Jacksonville, and Springfield are in the eastern part.
This area is underlain by Pennsylvanian shales, siltstones, and limestones in the southern and western parts and Ordovician and Silurian limestone in the extreme northern part. Coal beds occur in the northern part and east of the Illinois River.
The eastern part of the area, on the east side of the Illinois River, is on the glaciated Springfield Plain. The western part is dominantly on the Galesburg Plain. The northern part of this western area also encompasses the Green River Lowland and the Rock River Hill Country. The entire MLRA was glaciated and has deposits of loess of various thickness. The area is on a relatively young, moderately dissected to strongly dissected, rolling plain where stream terraces are adjacent to broad flood plains along the major streams and rivers.
Glacial drift covers the entire area, except for the bluffs along the major streams, where the underlying bedrock can be exposed. The glacial till is Illinoian in age and consists of distinct till units as well as sorted, stratified outwash of Wisconsin age. The entire area has been covered by a thick or moderately thin layer of Wisconsin loess. In a few areas the loess directly overlies the bedrock.Topography -
Elevation ranges from 660 feet (200 meters) in the eastern and southern parts of the area to about 985 feet (300 meters) in the western and northern parts.
Relief is typically is only 3 to 10 feet (1 to 3 meters) on the broad, flat uplands.
The maximum local relief is about 160 feet (50 meters) along the major streams and along the dissected drainageways fingering into the uplands.
The average annual precipitation in this area is 33 to 39 inches (840 to 990 millimeters).
Most of the rainfall occurs as high-intensity, convective thunderstorms during the growing season.
The average annual temperature is 47 to 54 degrees F (8 to 12 degrees C).
The freeze-free period averages about 185 days and ranges from 165 to 210 days.
* this is the percent of area drained by each named hydrologic unit
The Illinois, Rock, and Mississippi Rivers drain the MLRA.
|Public supply||surface water||46.8%||ground water||16.5%|
|Livestock||surface water||0.1%||ground water||4.1%|
|Irrigation||surface water||0.5%||ground water||7.2%|
|Other||surface water||20.6%||ground water||4.2%|
Total daily withdrawls average 240 million gallons per day (910 million liters).
32% Ground water sources
68% Surface water sources
The surface water is of fair or good quality and is suitable for most uses. Numerous large rivers provide surface water for this area. Water-supply reservoirs are common in the eastern part of the area.
Sediment, nutrients, and pesticides from agricultural activities and wastewater discharges from cities can contaminate the water.
The principal sources of ground water in this area are glacial drift, the Sand-and-Gravel aquifer, alluvial aquifers along the major streams, and Paleozoic bedrock.
Glacial drift aquifers have high levels of iron. The iron is not dangerous to public health, but it causes esthetic problems of iron stains and scale. Alluvial deposits are similar in quality to the surface water and is suitable for most uses. The shallow Sand-and-Gravel aquifer typically consists of glacial outwash deposits within the drift. Water in this aquifer is very hard and may have very high levels of iron. The median level of total dissolved solids is very near the national secondary drinking water standard of 500 parts per million (milligrams per liter).
Paleozoic bedrock aquifers are not utilized very much in this area. The Shallow Dolomite aquifer occurs only in the northern one-third of the western part of this area. Its water is similar in quality to the water in the Pennsylvanian- Mississippian aquifer, and it is not used unless no other aquifer is available.
The Pennsylvanian-Mississippian aquifer underlies all of the eastern part of the area and the southern two-thirds of the western part. Well yields from this aquifer are generally low, so the aquifer is not used extensively. The water in this aquifer is extremely variable in quality. It is generally more heavily mineralized than the water in the surficial aquifers, and it has high levels of iron.
The Cambrian-Ordovician aquifer occurs only north of the Shallow Dolomite aquifer in the western part of this area. This aquifer is used extensively in the northern third of Illinois. Its water is of good quality and is suitable for almost all uses. Wells can penetrate the St. Peter Sandstone in the upper part of this unit or the deeper Ironton-Galesville layer. The median level of total dissolved solids is typically less than the national secondary drinking water standard of 500 parts per million (milligrams per liter), and iron levels are much lower than those in the water from the other bedrock aquifers.
Most of the soils are Udolls or Udalfs. Aquolls are in the flatter interfluve areas. The soils are moderately deep to very deep and range from somewhat poorly drained to well drained and silty or clayey.
|Endoaquolls||Sable series||formed on broad interfluves.|
|Albaqualfs||Rushville and Denny series||formed on broad interfluves.|
|Argiudolls||Tama and Ipava series||formed in thick deposits of loess on uplands.|
|Hapludalfs||Fayette, Elco, and Hickory series||formed in loess that is deep to loamy till or a paleosol along the major streams and in dissected upland drainageways.|
|Marseilles series||formed in loess and bedrock residuum in major stream valleys.|
|Argiudolls||Plano and Warsaw series||formed on gently sloping to sloping terraces along the major streams.|
|Hapludalfs||St. Charles and Fox series||formed on gently sloping to sloping terraces along the major streams.|
|Endoaquolls||Sawmill and Otter series||formed in alluvium on nearly level, broad flood plains.|
|Hapludolls||Lawson, Huntsville, and Ross series||formed in alluvium on nearly level, broad flood plains.|
|Fluvaquents||Wakeland series||formed along the much smaller upland drainageways.|
|Udifluvents||Orion series||formed along the much smaller upland drainageways.|
This area originally supported prairie vegetation with hardwood forests on scattered upland sites. The areas of tall prairie grasses are characterized by big bluestem, Indiangrass, prairie dropseed, and switchgrass. White oak, shingle oak, black oak, hickory, white ash, basswood, sugar maple, and walnut grow on the better drained soils. Silver maple, black willow, cottonwood, and sycamore grow on flood plains.
Some of the major wildlife species in this area include whitetailed deer, coyote, turkey, red fox, beaver, raccoon, muskrat, opossum, cottontail rabbit, fox squirrel, Canada goose, red-tailed hawk, great horned owl, blue heron, wood duck, mallard duck, redheaded woodpecker, and quail.
|79% -||Cropland||- private|
|7% -||Grassland||- private|
|5% -||Forest||- private|
|6% -||Urban development||- private|
|1% -||Water||- private|
|2% -||Other||- private|
Cash-grain crops include corn for grain and silage, soybeans, winter wheat and oats. Hay and pasture crops also are grown for the livestock produced in the area.
About 7 percent of the area supports introduced and native grasses.
Surface-mined areas that have been or are being reclaimed occur in the northern part of the area and active underground coal-mining areas occur on the east side of the Illinois River.
Major resource concerns are wind erosion, water erosion, and maintenance of the content of organic matter and productivity of the soils.
Conservation practices include systems of crop residue management (especially no-till systems), cover crops, windbreaks, vegetative wind barriers, and nutrient management.