SURFICIAL MAP OF THE STREATOR SOUTH 7.5 MINUTE QUADRANGLE, LASALLE/ LIVINGSTON COUNTIES ILLINOIS

The Streator South 7.5 minute Quadrangle is located in Southern LaSalle and Northern Livingston Counties, Illinois between 88° 45' and 88° 52' 30” west longitude and 41° 00' and 41° 07' 30” north latitude. The purpose of this research project has been to construct a detailed surficial geologic map of the Streator North 7.5 minute Quadrangle at a 1:24,000 scale using current stratigraphic classification. This project has been a continuation of a state-wide effort to map at this scale. This has been achieved by using various techniques. Soil maps and descriptions found in the USDA Soil Survey maps were used to construct a preliminary geologic map. Based on each description the parent material of each soil type was determined. We then went into the field for hands-on mapping and interpretations of the well log data which were then checked against this initial map. Five stratigraphic units were identified in this area; Cahokia Alluvium (QHc), Peoria Silt (Qps), Equality (Qe), Lemont (Qly) and Carbondale Formations (Pc). The Cahokia Alluvium was found along the Vermilion River. The majority of the area consists of the Lemont Formation which is a massive red to gray diamicton. The Equality formation is red to gray bedded silt and clay. The Peoria Silt is massive yellow loess which is five or more feet thick. This is the least abundant of the Quaternary formations and is located sporadically throughout the entire area. Few outcrops of the Carbondale Formation bedrock were located along the Vermillion River. Funding for this research was provided by the Illinois State Geologic Survey and the United States Geologic Survey.