Potpouri of Geology at Pere Marquette, Part I EarthCache
Potpouri of Geology at Pere Marquette, Part I
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In Part I of this "Potpouri of Geology" I will take you to Pere Marquette State Park, near Grafton, Illinois.
As you enter the parking lot at the posted coordinates on the cache page you will see the lodge which sits on the “Brussels Terrace.” It took millions of years for the glacier outwash to form this plateau during the Illinoian age. Below the Brussels Terrace is the “Deer Plain Terrace” that was formed during the Wisconsin age and flows all the way to the existing road and beyond. This land slopes gently 15 to 20 feet per mile away from the base of the bluffs and was formed during the Wisconsin age. Your hike along Goat Cliff Trail will begin at the northwest end of the parking lot. Your starting point is at 38 58.420 N and 090 32.660 W. Within a short walking distance (about 300 yards) along this marked trail you will discover two significant geological features. At 38 58.557 N and 090 32.694 W you will see the results of the earth’s upheaval which brought the land up and out of an ancient sea nearly to its present level which in geological terms is called a “fault line.” This fault line is named the “Cap Au Gress.” At this coordinates you are looking at the limestone bluffs that were actually the floor of that ancient sea. When the earth moves with this much force cracks are formed, these cracks in the earth are called faults. This fault is visible from the path and it goes all of the way to the top of the rocks that you can see in front of you. At this point you are standing on the fault line! This fault runs east and west through the state of Missouri and then it turns south shortly after entering Illinois. This fault is responsible for the east and west direction that the Mississippi River takes in this area. You will also want to locate the “Benchmark” embedded in the rock at this location. Now, look below the path where you are standing to find the “Twin Springs” that are flowing into the creek. Further up the trail (less than 300 yards, at 38 58.654 N and 090 32.670 W) you will see an outcrop of rocks that stands vertically on the left side of the trail. If you look closely at the limestone rocks you will see some fossils of the ancient marine life (such as corals, sponges, trilobites, fish, snails, and clams) that lived in the shallow, warm, inland sea that once covered North America nearly 400 million years ago. I extend my sincere thanks and appreciation to Scott Isringhausen, Site Interpreter, for providing the geological information and to Pam Warford, Site Manager, for granting permission to establish and share in the excitement of developing an EarthCache at Pere Marquette State Park, Illlinois. Address: Pere Marquette State Park, 13112 Visitor Center, Lane, Grafton, IL 62037 Telephone Number: (618) 786-3323 Official Web Site: www.dnr.state.il.us (click to e-mail this site) TO LOG THIS FIND YOU MUST: Post a picture of yourself with your GPSr at the Fault Line and Twin Springs; DO NOT CLIMB THE ROCKS, STAY ON THE TRAIL, then click on my profile and e-mail the answers to the following questions to me. Do not post your answers when you log in your find. Logs which do not meet the requirements to claim the find will be deleted. 1) What is the elevation from where you are standing on the trail at the fault line and Twin Springs? 2) What is the "ESTIMATED" height of the bluff from where you are standing on the trail at the fault line and Twin Springs?
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