20261014 12450900 1.0 TRUE Quaternary_Deposits_500K_1979 Digital representation of the Quaternary Deposits in Illinois map by Lineback (1979). Map scale is 1:500,000. Shows Quaternary deposits that lie at or near the land surface, including loess deposits. J.A. Lineback, Illinois State Geological Survey geology quaternary surficial loess silt sand gravel till alluvium colluvium Illinois ISGS Quaternary Deposits in Illinois. Map scale is 1:500,000. Shows Quaternary deposits that lie at or near the land surface, including loess deposits.