SURFICIAL GEOLOGIC MAP OF SPRING VALLEY 7.5’ QUADRANGLE, LASALLE, PUTNAM, AND BUREAU COUNTIES, ILLINOIS

The Spring Valley 7.5’ Quadrangle occupies the area between 89º07’30” and 88º15’ west longitude, and 41º15’00” and 41º22’30” north latitude. The quadrangle includes the towns of Peru, Spring Valley, Granville, Standard, Cedar Point, and Dalzell. The principal drainages in the area are the Illinois River, Cedar Creek, All Forks Creek, and Spring Creek. A surficial geologic map was constructed using borehole and coal data from ISGS, soils map, surficial geologic observations, and geophysical data. This research was supported by grants from the US Geological Survey EDMAP and Illinois State Geological Survey Workforce Development programs.

The Spring Valley Quadrangle occurs west of the fore limb of the strongly asymmetric LaSalle Anticlinorium, and Paleozoic strata dip gently to the west. The Illinois River flows east to west near the center of the Quadrangle. Most rock and sediment exposures occur within the Illinois River Valley walls. The river dissects the Bloomington Ridged Plain, which is characterized by low, broad, morainal ridges of Woodfordian age separated by wide, comparatively flat lacustrine plains. The mouth of the Ticona Channel, a major pre-Wisconsin buried bedrock valley occurs in the southern part of the Quadrangle.

The bedrock stratigraphy in this area consists of the Pennsylvanian Bond and Mattoon Formations. The older Bond Formation is mainly green and red shale, but includes the prominent La Salle Limestone member containing medium gray fossiliferous limestone, medium to dark grayish green mudstone, and medium gray grainstone, and averages about 10 m (30 ft) in thickness. The Mattoon Formation consists of limestone with interbedded shale, coal, sandstone, and some clay, which averages about 3 m (10 ft) thick.

The Quaternary strata includes Illinoian and Wisconsinan sediments. The Illinoian consists of the Pearl Formation which averages 20 m (60 ft) in thickness and consists of sand, silt, and some gravel beds. The Wisconsinan units consist of Richland Silt, a 1 m (3 ft) veneer of loess, and clay rich till of Lemont and Tiskilwa Formations within the Wedron Group. These tills consist of gray to red-brown diamicton, and each are about 6-8 m (20-25 ft) in thickness. Sands and silts of the Cahokia Formation occur along the Illinois River.