Unconsolidated deposits, mainly glacial drift, overlie the bedrock surface in most of Illinois. Glacial drift ranges from less than a few feet to approximately 600 feet in thickness. The thickest drift occurs in major preglacial valleys cut into the bedrock and filled with glacial sediments. Regionally thick drift occurs in the N.E. portions of the state. The thinnest drift, less than 25 feet thick and intersected by numerous bedrock outcrops, occurs widely in southern and western portions of the State. Drift, as shown on this map, may include any of the following: unconsolidated deposits, glacial drift, Wisconsinan deposits, Illinoian deposits, till, glaciofluvial deposits, glaciolacustrine deposit, wind-blown deposits (loess).
The data are not appropriate as a geodetic, legal or engineering base. The data set was not and is not intended as a substitute for surveyed locations, such as can be determined by a registered Public Land Surveyor. Although useful in a GIS as a reference base layer for maps, the data set has no legal basis in the definition of boundaries or property lines.
In April 2004 edition 2.0 of the data set was transitioned to storage in an Oracle RDBMS using the ArcSDE geodatabase model. The result (this version) is designated Edition 20040423.
Edition 1.0 of this data set was replaced edition 2.0 in June, 1998. The data were reviewed as described in the logical consistency report and process steps for May, 1998. Contour values, which were not included in edition 1.0, were included in version 2.0.
Any hardcopies utilizing DNR data sets shall clearly indicate their source. If the licensee has modified the data in any way they are obligated to describe the types of modifications they have performed on the hardcopy map. Licensee specifically agrees not to misrepresent DNR data sets, nor to imply that changes they made were approved by DNR.
Some changes were made, as follows:
Arcs were coded with contour values. This was done with an AML program that assigned contour values to arcs based on the drift thickness values for the adjacent polygons. This processing was done in late 1996, but the updates were not posted to the general-use data set until June of 1998.
The features were imported into the ISGS SDE enterprise database following steps outlined in ISGS procedure GISDB_0009.
Metadata updated.
Polygon Attributes: THICK - thickness of drift 1 - Less than 25 feet 2 - 25 to 50 feet 3 - 50 to 100 feet 4 - 100 to 200 feet 5 - 200 to 300 feet 6 - 300 to 400 feet 7 - 400 to 500 feet 8 - Greater than 500 feet Thick. 9 - No Drift (Driftless Regions)
RANGE - range of thicknesses in feet for that polygon
Arc Attributes: CONTOUR - The contour value for the arc. Values of 999 indicate a line that is not a contour.
In no event shall the DNR have any liability whatsoever for payment of any consequential, incidental, indirect, special, or tort damages of any kind, including, but not limited to, any loss of profits arising out of use of or reliance on the geographic data or arising out of the delivery, installation, operation, or support by DNR.