SURFICIAL AND BEDROCK GEOLOGIC MAPPING IN LINN COUNTY, IOWA: IOWA'S CONTRIBUTION TO THE STATEMAP PROGRAM

by
E.A. Bettis, III, G.A. Ludvigson, J.D. Giglierano, M.R. Howes, and R.R. Anderson

The Geological Society of America
30th Annual North-Central Section Meeting
Iowa State University, Ames, IA May 2-3, 1996
1996 Abstracts with Programs, v. 28, no. 6, p. 29

ABSTRACT


The Iowa DNR-GSB is involved in the second year of a three-year program to map the near-surface geology of Linn County as part of the STATEMAP Program administered by the U.S. Geological Survey. Quadrangle-scale mapping has focused in and around the Cedar Rapids metropolitan area and in the Central City Quadrangle, while 1:100,000 scale bedrock mapping has been county wide. Quadrangle map areas were selected to address concerns about karst, well-head protection, the need for an additional sanitary landfill location, and industrial and suburban expansion.

Surficial mapping focuses on the upper five meters and uses subsurface information derived from water well records, engineering boring logs, research cores and auger holes, and outcrops (natural and excavations), as well as surface topography, tonal patterns from aerial imagery, and published soil survey information to map the distribution of 19 units that include the range of geologic materials (including anthropogenic sediments) found in the county. Bedrock mapping employs similar methods to map the distribution of the county's Pennsylvanian, Devonian and Silurian rocks at the formation level.

Mapping is done on screen using ArcView 2.0 software and all data points are geo-referenced. On-screen mapping allows geologists to concurrently view topography, photographic images of the map area (digital orthophoto), soil information, data points, and their associated geologic information, while drawing geologic contacts. This results in a better, more time- and cost-efficient, and more easily updated product than maps constructed by hand. An additional advantage to the production of digital coverages is that information from geologic and other databases can be easily combined to produce coverages (derivative maps) for addressing a wide range of environmental and social issues.