Most of this area is in the glaciated Till Plains Section of the Central Lowland Province of the Interior Plains.
The southeast corner is in the Highland Rim Section of the Interior Low Plateaus Province of the Interior Plains.
63% of this area within Indiana.
37% of this area within Illinois.
Total Land Area 3,690 square miles (9,565 square kilometers).
Evansville, Sullivan, Vincennes, Princeton, and parts of Terre Haute, Indiana.
Marshall, Newton, Robinson, Lawrenceville, Olney, Mt. Carmel, Carmi, and Shawneetown,, Illinios.
The George Rogers Clark National Historic Park, Harmonie State Park, New Harmony State Memorial, and Hovey Lake
State Game Reserve are in the part of the area in Indiana.
Lincoln Trail State Park is in the part in Illinois.
Pennsylvanian-age bedrock underlies this area. Bedrock outcrops are common in the walls of the valleys along the Wabash and Ohio Rivers and at the base of some steep slopes along minor streams and drainageways.
This area is covered almost entirely with Wisconsin loess. The loess can be more than 7 feet (2 meters) thick on stable summits. On the steeper slopes, it is thin or does not occur. The loess throughout the area is underlain dominantly by glacial till. Wisconsin outwash, alluvial deposits, and sandy eolian material are on some of the stream terraces and on dunes along the major tributaries in the area.Topography -
Elevation ranges from 320 to 1,020 feet (100 to 310 meters). Relief is typically 10-50 feet (3 - 15 meters). In the steeper, deeply dissected hills bordering rivers, the relief can be 50 to 100 feet (15 - 45 meters).
The average annual precipitation in this area is 40 to 47 inches (1,015 to 1,195 millimeters).
Most of the rainfall occurs as high-intensity, convective thunderstorms.
The average annual temperature is 53 to 57 degrees F (11 to 14 degrees C).
The freeze-free period averages about 210 days and ranges from 200 to 225 days.
* this is the percent of area drained by each named hydrologic unit
|Public supply||surface water||30.1%||ground water||0.6%|
|Livestock||surface water||0.1%||ground water||0.2%|
|Irrigation||surface water||0.2%||ground water||0.2%|
|Other||surface water||93.1%||ground water||2.6%|
Total daily withdrawls average 855 million gallons per day 3,235 million liters).
4% Ground water sources
96% Surface water sources
The larger rivers provide water for industrial and municipal uses and for some limited irrigation. Surface waters are suitable for almost all uses.
Abundant ground water occurs only in deposits of unconsolidated sand and gravel along the Ohio River, the lower White River, and the Wabash River. The average values of total dissolved solids are close to 500 parts per million (milligrams per liter).
Away from the river valley deposits, ground water in Illinois comes from the Pennsylvanian-Mississippian aquifer. The level of total dissolved solids is 500 to 3,000 parts per million (milligrams per liter).
In Indiana, the only other source of ground water is in isolated lenses of sand and gravel buried in older glacial till outside the river valleys.
The soils are very deep, poorly drained to excessively drained and loamy, silty, or clayey.
|Endoaqualfs||Iva series||formed in loess on broad upland summits and flats.|
|Argiaquolls||Ragsdale series||formed in loess on broad upland summits and flats.|
|Hapludalfs||Alford, Iona, Muren,Stoy, Sylvan series||formed in loess on uplands.|
|Fragiudalfs||Hosmer series||formed in loess on uplands.|
|Hapludalfs||Alvin, Bloomfield, Princeton series|
|Argiudolls||Ade series||formed in sandy eolian material in areas of dunes on uplands and stream terraces.|
|Hapludalfs||Wellston series||formed in siltstone or sandstone residuum on strongly sloping to steep side slopes underlain by bedrock.|
There are many other soil series listed in the USDA information.
The uplands in this area support natural hardwoods. Oak, hickory, and sugar maple are the dominant species. Big bluestem, little bluestem, and scattered oak trees grow on some sites.
The lowlands support mixed forest vegetation, mainly elm, cottonwood, river birch, ash, silver maple, sweetgum, sycamore, pin oak, pecan, and willow. Sedge and grass meadows and scattered trees are on some lowlands.
Some of the major wildlife species include whitetailed deer, gray and red fox, beaver, mink, raccoon, opossum, great horned owl, bobwhite quail, and wood duck.
|69% -||Cropland||- private|
|6% -||Grassland||- private|
|13% -||Forest||- private|
|6% -||Urban development||- private|
|3% -||Water||- private|
|3% -||Other||- private|
Winter wheat, corn, soybeans, grain sorghum, and other feed grains are the principal crops. Specialty crops include melons, potatoes, apple and peach orchards. Some surface coal mining occurs in this area.
The major resource concerns include wind and water erosion, flooding, wetness; maintenance of the content of organic matter in the soils and productivity of the soils.
Conservation practices on cropland generally include surface and subsurface drainage systems, crop residue management, filter strips, cover crops, and nutrient and pest management. Woodland management practices, such as exclusion of grazing and timber stand improvement, are important for timber production.