-11- 



a position, the ice margin contributed most of its meltwater to the valley of 

 the Kankakee River about 40 miles southeast of here, whence it flowed into 

 the Illinois. At the height of the flood, which was named the Kankakee Flood 

 (Willman and Frye, 1970), waters backed up between moraines and formed several 

 large lakes: Lake Ottawa, Lake Pontiac, Lake Wauponsee, and Lake Kankakee. As 

 floodwaters slackened, the valley of the Illinois was cut to the level of the 

 top of Starved Rock. 



The second stage of downward cutting took place when glacial Lake 

 Chicago, the ancestor of present-day Lake Michigan, overflowed down the 

 valley, deepening it approximately another 60 feet in the interval from 

 about 13,500 to 3,000 years ago. Lake Chicago resulted from the trapping 

 of water between the Tinley Moraine on the back side of the Valparaiso Morainic 

 System and the front of the glacier that occupied the Lake Michigan Basin. 

 The Ottawa Terrace represents the lowest level cut by the Chicago Outlet 

 River. A deep groove low in the cliffs of Starved Rock and Buffalo Rock 

 marks the level of the floodwaters. Since then, the modern river has cut 

 its inner valley another 30 feet to reach its present level. 



In the upper part of several valleys in the park, the Cheltenham Clay 

 Member of the Pennsylvanian Spoon Formation can be seen underlying the Col- 

 chester (No. 2) Coal Member. 



Mileage 



Adjust odometer. Leave parking lot in convoy. 



00.00 Turn left (south) onto road. 



Left turn (east) . 



Right turn toward valley wall. 



STOP SIGN. Climb steep hill. 



Road on left leads to Lodge. Continue straight ahead. 



STOP SIGN. Junction with Illinois Route 71. Turn right 

 (west) on Route 71. 



00.05 



00.05 



00.25 



00.20 



00.35 



00.10 



00.75 



00.40 



01.25 



00.50 



02.05 00.80 



Junction with Illinois Route 178, 

 straight ahead. 



Do not stop. Continue 



03.55 01.50 



We are crossing over the crest of the La Salle Anticline. 

 The structure, which consists of a broad, nearly monoclinal 

 fold, has a westerly dip of about 2000 feet per mile and 

 an easterly dip of about 25 to 50 feet per mile. North- 

 westward from here it trends S. .24° E. Southwestward from 

 here it trends S. 15° E. The anticline is the largest 

 structural feature in northeastern Illinois and marks the 

 northeastern limit of the Illinois Basin. 



