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| Cahokia Plain | |
|---|---|
| Name | Cahokia Plain |
| Settlement type | Geographical plain |
| Subdivision type | Country |
| Subdivision name | United States |
| Subdivision type1 | State |
| Subdivision name1 | Illinois |
| Subdivision type2 | County |
| Subdivision name2 | St. Clair County |
Cahokia Plain is a low-lying alluvial plain in southwestern Illinois adjacent to the Mississippi River and the American Bottom. The plain encompasses a mosaic of archaeological sites, agricultural fields, wetlands, and urbanizing corridors near St. Louis. It has played a central role in continental prehistory, nineteenth-century settlement, and contemporary conservation debates involving local, state, and federal agencies.
The Cahokia Plain occupies part of the larger American Bottom floodplain between the Mississippi River and the bluffs of the Mississippi River Valley, bounded to the north by the Kaskaskia River lowlands and to the south by the Cahokia Creek watershed. Major municipalities and places on or near the plain include Cahokia Heights, Illinois, Collinsville, Illinois, East St. Louis, Illinois, and suburban sectors of Greater St. Louis. Transportation corridors crossing the plain include the Interstate 55, Interstate 64, and multiple historic rail lines associated with the Illinois Central Railroad. Hydrological features such as the Kaskaskia River Floodplain and engineered channels related to the Chain of Rocks Canal define local boundaries and influence land use.
Geologically, the plain consists of Pleistocene and Holocene alluvium deposited by episodic flood events of the Mississippi River and tributaries, overlaying bedrock from the Ordovician and Silurian sequences exposed in nearby bluffs. Soils are predominantly alluvial loams and silty clay loams classified within series used for intensive agriculture by the United States Department of Agriculture soil surveys. Fluvial terraces and backswamps create heterogeneity in sediment stratigraphy; subsurface cores reveal sequences correlated with regional stratigraphic frameworks established by the United States Geological Survey and academic studies from University of Illinois Urbana–Champaign and Southern Illinois University. Post-glacial loess mantles are thinner here than on the Missouri River terraces, but local aeolian deposits affect drainage and fertility patterns.
Archaeological investigations on the plain document continuous human occupation from Paleoindian and Archaic period camps through Woodland and Mississippian chiefdoms linked to regional interaction spheres such as the Mississippian culture and the wider Eastern Woodlands tradition. Excavations by teams affiliated with Franklin D. Roosevelt Presidential Library-era programs, later university field schools, and the Smithsonian Institution uncovered habitation sites, shell middens, and ceremonial structures. Radiocarbon sequences calibrated against standards maintained by the International Radiocarbon Laboratory frame occupational phases contemporaneous with sites like Kincaid Mounds and Etowah Mounds. Artifact assemblages include regional lithic types, pottery tempering traditions tied to the Northeastern Woodlands, and trade goods reflecting exchange with groups along the Ohio River and Gulf Coast.
The Cahokia Mounds site, a UNESCO-designated World Heritage Site component within the plain, anchors a cultural landscape of plazas, earthworks, and burial mounds attributed to an urbanizing Mississippian polity. Monumental features such as Monks Mound and the Grand Plaza relate to cosmological models documented in comparative studies of Moundville Archaeological Park and Poverty Point. Site management involves partnerships among the Illinois Historic Preservation Agency, National Park Service, and local tribal nations including the Iowa Tribe of Oklahoma and Osage Nation who engage in interpretation and consultation. Research on sociopolitical complexity, craft specialization, and agricultural intensification at Cahokia informs broader debates in archaeology about chiefdoms described in works from the American Anthropological Association community.
Euro-American settlement transformed the plain after treaties such as the Treaty of Greenville-era dispossessions, agricultural expansion, and nineteenth-century transportation improvements including steamboat routes associated with Robert Fulton-era river commerce. Nineteenth- and twentieth-century land use shifted between corn and soybean agriculture, levee construction by engineers from the U.S. Army Corps of Engineers, and urban-industrial development tied to St. Louis markets. Industrial facilities, rail yards, and suburban subdivisions altered hydrology and soil profiles; state and county planning documents from Madison County, Illinois and St. Clair County, Illinois reflect zoning changes and infrastructure investment.
Native ecological communities on the plain included bottomland hardwood forests dominated by species abundant in regional floras curated by the Missouri Botanical Garden and the Field Museum of Natural History. Wetland mosaics supported migratory waterfowl linked to the Mississippi Flyway and aquatic assemblages studied by researchers from Illinois Natural History Survey. Habitat fragmentation, invasive species documented by the Illinois Invasive Species Council, and altered flood regimes changed ecological trajectories. Remnant habitats sustain populations of amphibians and floodplain birds noted in surveys by the Audubon Society chapters in the region.
Conservation and management involve coordination among the Illinois Department of Natural Resources, National Park Service, tribal governments, and non-governmental organizations like The Nature Conservancy. Threats include river engineering projects authorized under statutes administered by the U.S. Army Corps of Engineers, suburban sprawl from St. Louis Metropolitan Area growth, looting and vandalism addressed under the National Historic Preservation Act, and climate-driven changes in flood frequency examined in studies from National Oceanic and Atmospheric Administration. Ongoing mitigation combines archaeological stewardship, wetland restoration, and land-protection strategies funded through programs of the U.S. Fish and Wildlife Service and state conservation grants.
Category:Plains of Illinois Category:Mississippi River