This layer consists of a polygon coverage at 1:500,000 scale with information about bedrock type used in the GCSM. Bedrock is the consolidated material that underlies the soils and surficial deposits; 'bedrock type' is defined as type of the uppermost rock layer. Bedrock type is important in assessing an area's susceptibility to groundwater contamination, especially if the bedrock is located close to the land surface. The source for this layer is the set of 1:500,000- scale compilation sheets for a 1981 map of bedrock geology of Wisconsin published by the WGNHS. Because of the generalized nature of the GCSM project, bedrock types were grouped into 4 categories during automation of this data layer.