region M Area 108 C larger picture

Illinois and Iowa Deep Loess and Drift, West-Central Part

Dissected Till Plains Section of the Central Lowland Province of the Interior Plains.

Area entirely in Iowa.

Total Land Area 9,805 square miles (25,405 square kilometers).

Towns/cities include:
Newton, Oskaloosa, Pella, Marshalltown, Iowa City, and Washington

The Sac and Fox and Mesquakie Indian Reservations are in this area.

This area also includes many State parks

Geology

Paleozoic bedrock consisting dominantly of limestone, shale, and mudstones. The bedrock includes dolomite in the northeastern part of the area. Locally, it is within a landform region called the Southern Iowa Drift Plain. As the section name implies, this area is a dissected till plain.

This area is underlain by dense pre-Illinoian till, which was deposited more than 500,000 years ago and has since undergone extensive erosion and dissection. The till surface is covered by a mantle of Peoria Loess on the hillslopes and by Holocene alluvium (DeForest Formation) in the drainageways. The till is generally less than 150 feet (45 meters) thick in the southern half of the area but ranges from 150 to 350 feet (45 to 105 meters) in thickness in the northern half.

Slopes are mostly rolling to hilly, but some broad ridgetops are nearly level to undulating and areas bordering the major stream valleys are steep. A few large rivers have nearly level, broad valley floors.

Topography -

Elevation ranges from 505 feet (155 meters) in the lowest valleys to 1,110 feet (340 meters) on the highest ridges.

Local relief is mainly 10 to 20 feet (3 to 6 meters).

Valley floors can be 80 to 200 feet (25 to 60 meters) below the adjacent uplands. Some upland flats and valley floors have local relief of only 3 to 6 feet (1 to 2 meters).

Climate

The average annual precipitation in this area is 33 to 38 inches (840 to 965 millimeters).
Most of the rainfall occurs as high-intensity, convective thunderstorms during the growing season.
The average annual temperature is 46 to 51 degrees F (8 to 11 degrees C).
The freeze-free period averages about 185 days and ranges from 170 to 205 days.

Major Hydrologic Unit Areas

Name Code Extent*
Upper Mississippi-Iowa-Skunk-Wapsipinicon (0708) 95%
Des Moines (0710 ) 5%

* this is the percent of area drained by each named hydrologic unit

The Des Moines, Skunk, Iowa, and Cedar Rivers cross this area. These watersheds have more than 10,600 miles of streams and associated wetlands that drain to the Mississippi River.

Water

Estimated withdrawls in this MLRA:
Public supply surface water 4.8% ground water 45.3%
Livestock surface water 4.2% ground water 17.1%
Irrigation surface water 0% ground water 0.5%
Other surface water 1.1% ground water 27%

Total daily withdrawls average 90 million gallons per day (340 million liters).
90% Ground water sources
10% Surface water sources

Large rivers provide some surface water and the Coralville Reservoir provides water to areas along the Iowa River.The surface water is of fair quality and is suitable for most uses with treatment.

Contamination from sediment, nutrients, and pesticides from agricultural activities and wastewater discharges from cities cause some water-quality problems.

The principal sources of ground water in the area are glacial drift aquifers, buried channel aquifers, alluvial aquifers, and Paleozoic bedrock. Glacial drift aquifers supply small quantities of water. Alluvial deposits provide much greater quantities of water. Buried channels typically consist of glacial outwash deposits that filled preglacial valleys and then were covered by glacial drift. Large quantities of water can be obtained from this aquifer in the limited areas where it occurs.

All of these surficial aquifers have good-quality water. The water is very hard and the median level of total dissolved solids is near the national secondary drinking water standard of 500 parts per million (milligrams per liter).

Paleozoic bedrock aquifers are heavily utilized in this area. The Silurian-Devonian aquifer underlies the northern half of the area, the Mississippian aquifer underlies the southern half, and the Jordan aquifer underlies all of the area.

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 Jordan aquifer is the most extensively used aquifer in Iowa. It consists of sandstone and dolomite of Ordovician and Cambrian age. Well yields from this aquifer are very high. The water from this aquifer is suitable for most uses, but the median level of total dissolved solids typically exceeds 800 parts per million (milligrams per liter) and radium-226 levels can exceed the national standard for drinking water.

The Silurian-Devonian aquifer consists of limestone and dolomite. It is close to the surface in this area, and has the best water quality of all the principal aquifers in Iowa. Where this aquifer is buried by younger bedrock deposits, its use is limited by the level of total dissolved solids and naturally high levels of sulfate.

The Mississippian aquifer consists of limestone and dolomite that is very close to the surface in this area. Its water quality is between that of the other two bedrock aquifers. In some areas it has very high levels of total dissolved solids and is not used. Wells in this aquifer produce low yields, so the aquifer is not used unless no other water sources are available.

Soils

  • Mesic soil temperature regime.
  • Aquic or udic soil moisture regime.
  • Mixed mineralogy.
  • Dominant Soils:

  • Mollisols
  • Alfisols
  • Entisols
  • Inceptisols
  • Most of the soils are Udolls or Udalfs. Aquolls are in the flatter interfluve areas and broad valley floors. The soils are very deep and range from well drained to poorly drained and silty, loamy, or clayey.

    Great Group Series Location
    Argiudolls Mahaska series formed on uplands including somewhat poorly drained, nearly level areas.
    Hapludolls Muscatine series formed on uplands including somewhat poorly drained, nearly level areas.
    Argiudolls Otley series formed on moderately well drained, gently sloping to strongly sloping areas.
    Eutrudepts Killduff series formed on well drained or moderately well drained, moderately sloping to strongly sloping areas
    Endoaquolls Garwin series poorly drained, nearly level areas.
    Argiaquolls Taintor series formed on well drained or moderately well drained areas.
    Argiudolls Tama and Dinsdale series formed on gently sloping to strongly sloping areas.
    Hapludalfs Fayette, Downs, Ladoga, Armstrong, and Clinton series formed on well drained, strongly sloping to steep areas.
    Hapludolls Lawson series formed in silty alluvium on flood plains.
    Udifluvents Nodaway series formed in silty alluvium on flood plains.
    Endoaquolls Colo and Zook series formed in clayey alluvium on flood plains.

    Fauna and Flora

    Prairies in this area are dominated by tall grasses. Xeric mid and short grasses occur on steep slopes, ridges, and sandy soils. Grama, muhly, lovegrass, dropseed, wild rice, threeawn, and wheatgrass may occur in the prairies, along with the dominant bluestems, Indiangrass, switchgrass, prairie cordgrass, and wildrye.

    The forbs in the area include pale and round-stemmed false foxgloves, Virginia snakeroot, golden corydalis, kittentails, shooting star, foxglove penstemon, cleft phlox, eastern and western prairie fringed orchid, blackeyed Susan, sneezeweed, puccoon, wild geranium, slender mountain mint, and bottle gentian.

    Wooded areas on uplands commonly support red oak, white oak, hackberry, and shagbark, mockernut, butternut, and bitternut hickories. Wooded areas on bottom land commonly support swamp white oak, pin oak, river birch, sycamore, cottonwood, willow, redbud, white ash, green ash, silver maple, and American elder.

    The wildlife species on the prairies in this area include plains leopard frog, tiger salamander, ornate box turtle, sixlined racerunner, slender glass lizard, smooth green snake, bull snake, western hognose, prairie king snake, massasauga rattlesnake, long-eared owl, northern harrier, wild indigo dusky wing, Baltimore checkerspot, regal fritillary, plains pocket mouse, spotted skunk, and bald eagle.

    The wildlife species in the wooded areas include the great-crested flycatcher, prothonitary warbler, ovenbird, Acadian flycatcher, scarlet tanager, Indiana bat, western fox snake, western worm snake, and Fowler’s toad.

    This MLRA has 91 threatened or endangered species or species of special concern. The watersheds in the area provide habitat for many rare and declining species, such as the least tern, piping plover, lake sturgeon, pirate perch, blacknose and Topeka shiners, pallid sturgeon, grass pickerel, bluntnose darter, pugnose minnow, freckled madtom, sheepnose, round pigtoe, spectacle case, yellow sandshell, strange floater, pistol grip, central newt, Blanding’s turtle, yellow mud turtle, and common musk turtle.

    Land Use

    76% - Cropland - private
    9% - Grassland - private
    1% - - Federal
    6% - Forest - private
    5% - Urban development - private
    1% - Water - private
    2% - Other - private

    In the mid-1800s, about 75 percent of this area was prairie. Forests made up 18.5 percent of the area; savannas, 5 percent; shrub lands, 1 percent; wetlands, 0.4 percent; and streams, 0.1 percent.

    Farms currently make up nearly all of this area. They produce cash crops, grain crops, and livestock.

    Major resource concerns are water erosion, depletion of organic matter in the soils, and poor water quality.

    Conservation practices include systems of crop residue management (especially no-till, strip-till, and mulch-till systems), cover crops, pest and nutrient management, grassed waterways, terraces, manure management, pasture and hayland planting, and grade-stabilization structures.


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