SURFICIAL GEOLOGIC MAP OF THE BLOOMINGTON WEST 7.5 MINUTE QUADRANGLE IN MCLEAN COUNTY, IL

This study involved constructing a surficial geologic map of the 7.5 minute Bloomington West Quadrangle located in McLean County. The Quadrangle is confined within the area 89°00’ to 89°07’30” latitude and 40°30’ to 40°22’30” at a scale of 1:24,000. The sediments present were deposited during, and after the Wisconsin Glacial Episode. Methods used in the creation of the Quadrangle include the conversion of soilds data, LiDAR data, well water log data and field work. The five formations located in the Blooming West Quadrangle are the Cahokia, Tiskilwa, Lemont, Peroia and Henry. These formations are Quaternary in age. The Cahokia Alluvium is a silty clay interbedded with a fine sand and is located along stream beds and valley floors. The Cahokia Alluvium is interpreted to be post-glacial loess and till that has been redeposited in fans where streams and ravines emerge from uplands and onto low-slope valley floors. The Tiskilwa is a red-grey to grey calcerous clay loam. The Normal Moraine divides the Bloomington West Quadrangle with the Lemont being to the North and Tiskilwa to the South. The Lemont is a diamicton consisting of grey, blue, brown, black, and green clay interpreted to be a combination of silty loess and loamy till. The Peoria Silt is light yellow tan to grey sandy silt interpreted to be mostly a pro-glacial loess. The Peoria Silt is only mapable with a thickness of loess greater than sixty inches and comes from glacial meltwater channels. Lastly, the Henry Formation is gravel and sand interpreted to be valley train outwash.