SURFICIAL GEOLOGY OF ROCK ISLAND COUNTY, ILLINOIS

The surficial geology of Rock Island County initially was mapped by the late Richard C. Anderson, professor at Augustana College and affiliated with Illinois State Geological Survey (ISGS) primarily in the 1970s and 1980s. These 1:24,000-scale quadrangle maps were subsequently digitized and compiled by Barbara J. Stiff and staff at the ISGS. The compilation of this map, legend and text were finalized by Xiaodong Miao, so were the addition of sites of the aggregate production. Base map is from Light Detection and Ranging (LiDAR) data but LiDAR data are not used for mapping contacts. This map provides a general view of surficial geology.

Rock Island County, Illinois, contains a variety of geological deposits underlying floodplains, sloped valley sides, and level uplands. The landscape of the county has been shaped by three major geological agents: continental glaciers, rivers and wind. These agents were all active during the Pleistocene and Holocene Epochs, together known as the Quaternary Period. Human activities (such as quarry mining) also have modified the landscape of the county but in minor roles. Bedrock consists of Pennsylvania mudstone, siltstone and shale, Devonian limestone, Silurian dolomite, lying on granitic rock of Precambrian age.