SURFICIAL GEOLOGY OF THE STREATOR NORTH 7.5 MINUTE QUADRANGLE

The Streator North 7.5 minute Quadrangle is located in LaSalle County Illinois between 88° 45' and 88° 52' 30” west longitude and 41° 15' and 41° 07' 30” north latitude. The purpose of this research was to construct a detailed surficial geologic map of the Streator North 7.5 minute Quadrangle at a 1:24,000 scale using the current stratigraphic classification. This project was a continuation in an effort to map all of LaSalle County at this scale. This was accomplished using a combination of techniques. Soil maps and descriptions found in the USDA Soil Survey maps were used to construct an initial geologic map. Based on each description, the parent material of each soil type was determined Traditional field mapping and interpretations of well log data were then used to check 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 and Prairie Creek. 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. This formation is mainly located in the northeastern and southwestern portions of the map. The Peoria Silt is massive yellow loess which is five or more feet thick. This is the sparsest of the Quaternary formations and is located in small sections 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.