Quaternary Geologic Atlas of the United States

Example of the Mapping

USGS Quaternary Geologic Map of the Chicago 4° x 6° Quadrangle I-1420 (NK-16)

The surficial deposits are distinguished on the basis of environment of origin (genesis), grain size (texture), mineral and clast composition, stratigraphic relations, and age. The arcuate pattern of map units shows the distribution of glacial till (end moraine and ground moraine) of late Wisconsin age in parts of Wisconsin, Illinois, and Indiana. Grain size or textural differences in the till matrix (clayey vs. loamy vs. sandy loamy) are indicated by different colors and letter symbols; end moraine and ground moraine are distinguished by different shades of the same color. Most of the area in the northwest corner here (mapped as colluvium and sheetwash alluvium) was not glaciated. The area between the "Driftless Area" and the arcuate moraines is chiefly till of pre-Wisconsin age. Extensive areas of glaciofluvial deposits (outwash), glacial lake deposits, windblown deposits, and alluvium also are mapped.

Map units are distinguished on the basis of:

• Physical, chemical, sedimentologic, and (where available) engineering properties
• Environment of origin (e.g., volcanic rocks, alluvial, eolian, lacustrine, marine, colluvial, or glacial deposits; residual materials)
• Stratigraphic relations
• Age

Important stratigraphic sections and paleontologic sites, and also features or phenomena such as faults with Quaternary displacement, dune fields, paleowind directions, volcanic ash sites, glaciotectonic phenomena, drumlins, buried bedrock valleys, and limits of past glaciations and glacial advances are shown as symbols on some maps.

On some quadrangles, geologic hazards are mapped (e.g., faults with Quaternary displacement; landslide deposits or landslide-prone surficial deposits and materials; volcanic rocks and related deposits). In some regions, sediments (such as till) that contain significant swelling clay are distinguished from similar sediments that contain little or no swelling clay.

Natural resources such as clay, peat, and coquina are mapped, as are rocks, deposits, and materials used as aggregate.

The Quaternary Period includes the time of all activities of man. Some maps show areas of man-modified land (e.g., surface mines, mine tailings and spoil, settling ponds, artificial fill, and reclaimed land). The rocks, deposits, and materials mapped in most regions are the surface mantle of the earth, in which man's activities are concentrated. Because the map units are distinguished in part on the basis of physical, chemical, sedimentologic, and engineering properties, the maps provide a regional database of interest to scientists who are concerned with shallow groundwater aquifers, soil and groundwater contamination and pollution, and toxic and other shallow waste disposal. Many of the map units are closely related to soils as recognized in engineering geology, and to substrata or parent materials of agricultural soils. Consequently, the maps have direct relevance to engineering construction, land-use planning, land management, and current and future environmental problems and decisions.

A regional database for interpretation and reconstruction of past environments and climatic changes, and also for documentation of modern climatic and environmental conditions is provided by mapping of:

• Deposits and materials that have climatic/environmental implications (e.g., windblown sand, loess, floodplain alluvium, sheetwash alluvium, beach deposits, swamp and marsh deposits, glacial deposits, solifluction deposits, colluvium, solution and disintegration residuum, saprolite)
• Areas of intense erosion (e.g., deflation basins and badlands)
• Other deposits and phenomena of climatic/environmental significance

The maps provide a database for scientific reconstruction of regional geologic history. Because map units are distinguished on the basis of genesis (environment of origin), stratigraphic relations, and age differences, and because the units on each map are placed in a stratigraphic and chronologic framework, regional sequences of geologic events can be interpreted.

Collaborators for Published Maps

• Arkansas Geological Commission
• College of Wiliam and Mary
• Florida Geological Survey
• Geological Survey of Alabama
• Geological Survey of Canada
• Georgia Geological Survey
• Illinois State Geological Survey
• Indiana Geological Survey
• Iowa Geological Survey Bureau
• Kansas Geological Survey
• Louisiana Geological Survey
• Maine Geological Survey
• Manitoba Department of Energy and Mines
• Maryland Geological Survey
• Minnesota Geological Survey
• Mississippi Office of Geology
• Missouri Department of Natural Resources
• Montana Bureau of Mines and Geology
• Nebraska Conservation and Survey Division
• New York State Geological Survey
• North Carolina State University
• North Dakota Geological Survey
• Ohio State University
• Oklahoma Geological Survey
• Ontario Geological Survey
• Pennsylvania Topographic and Geologic Survey
• Princeton University
• Québec Ministère des Richesses Naturelles
• Saskatchewan Research Council
• Slippery Rock State College, Pennsylvania
• South Dakota Geological Survey
• Syracuse University, New York
• Tennessee Department of Conservation
• Texas Bureau of Economic Geology
• University of California
• University of Connecticut
• University of Maine
• University of Massachusetts
• University of Michigan
• University of Nebraska
• University of North Carolina
• University of South Carolina
• University of Vermont
• University of Virginia
• University of West Virginia
• University of Wisconsin
• Wisconsin Geological Survey

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