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Cahokia Mounds, a World Heritage Site

Hidden : 9/2/2008
In Illinois, United States
1 out of 5
1 out of 5

Size: Size: other (other)

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Geocache Description:

This is an EarthCache. The coordinates will take you to the starting point where a color coded marker directs you to a wheelchair accessible trail.

In 1982, the United Nations Educational, Scientific and Cultural Organization designated Cahokia Mounds a U.S. World Heritage Site for its significance in the prehistory of North America. This State Historic Site was named a U.S. National Historic Landmark in 1965.

“Managed by the Illinois Historic Preservation Agency, Cahokia Mounds State Historic Site, in Collinsville, Illinois, it is located on the Mississippi River floodplain, across from St. Louis, Missouri. This site was first inhabited by Indians of the Late Woodland culture about AD 700. The site grew during the following Mississippian period, after AD 900, and by AD 1050-1150, the Cahokia site was the regional center for the Mississippian culture with many satellite communities, villages and farmsteads around it. After AD 1200, the population began to decline and the site was abandoned by AD 1400. In the early 1600s, the Cahokia Indians (of the Illinois confederacy) came to the area and it is from them that the site derives its name.

However, it is the building accomplishments and cultural developments of the earlier Indians that make this site significant. They constructed more than 120 earthen mounds over an area of six square miles, although only 80 survive today. These industrious people moved over an estimated 55 million cubic feet of earth in woven baskets to create this network of mounds and community plazas. Monks Mound, for example, covers 14 acres, rises 100 feet, and was topped by a massive 5,000 square-foot building another 50 feet high. As the largest prehistoric earthen construction in the Americas, Monks Mound is a testament to the sophisticated engineering skills of these people. Additionally, they built several “Woodhenges,” large post-circle monuments that appear to have been used as calendars, and they also constructed several defensive palisades nearly two-miles long around the central ceremonial precinct.”

- U.S. World Heritage Sites, National Park Service,
U.S. Department of the Interior


It is hard to imagine that the Mississippi Valley was first covered by a sea over 500 million years ago when hard-shelled marine organisms first evolved. Many transgressions and regressions of the sea occurred depositing a variety of sedimentary rocks, most of which are now buried. Scientists estimate during the early Mississippian Period, about 350 million years ago, this area was once again covered by a shallow sea. Ancient organisms such as crinoids, corals, brachiopods, trilobites and bryozoans are now fossilized in the many layers of limestone. During the time of the Ice Age the northern portions of North America were periodically covered by glaciers. The Ice Age began 1.65 million years ago and ended approximately 10,000 years ago. The ice sheets reached 13,000 feet in thickness, causing the global sea level to drop about 300 feet below it’s current level because so much water was in the form of ice. Glaciers flowed southward from Hudson Bay between the Rocky and Appalachian Mountains and extended as far south as southern Illinois. As glaciers moved slowly over thousands of years, the huge amounts of ice changed the landscape, leveling and filling valleys, revealing the flat prairies that we see today. The great breadth of the floodplain is due to the large volume of glacial melt water that flowed through this river valley in the waning stages of the Ice Age.

It was this floodplain and access to the Mississippi River through it’s tributaries that gave the prehistoric Indians of the Late Woodland culture, about AD 700, and the Mississippian period that followed, after AD 900, the necessary resources to sustain life and develop a culture with many satellite communities. At its peak Cahokia had a population between 10-20,000 people. It is estimated that there were as many as 50,000 people living on farmlands, villages and small towns, in the American Bottoms which runs from Alton, Illinois to Dupo, Illinois. Highly structured communities arose with a complex ranked social and political system. Without this fertile floodplain they would not have been able to grow their primary crops of corn, squash and several oily and starchy seed bearing plants (sunflower, marshelder, lambs quarter, may grass, knotweed, little barley). The tributaries gave them access to the mighty Mississippi and they developed an extensive trade network with distant areas of the country.

- I used the internet to access sources by using google search to obtain information for this EarthCache. I also visited the site at Cahokia Mounds and gained a wealth of information from their Historic Site Interpreter.

The Treasure you Find is in the
Lessons you Learn.

Leave No Trace !!!

Many thanks to Mark E. Esarey, Ph.D., Cahokia's Site Manager, for granting approval, and to Marilyn Harvey, Cahokia’s Historic Site Interpreter, for supplying information and share in the excitement of having an EarthCache at the Cahokia Mounds State Historic Site.

Their official website is:
Telephone number: (618)346-5160
Address: Cahokia Mounds
30 Ramey Street
Collinsville,IL 62234

The Interpretive Center is open Wednesday thru Sunday from 9:00 am to 5:00 pm. The grounds are open from dawn until dusk. There is a small suggested donation fee. The coordinates will take you to the starting point outside of the center, which is wheelchair accessible.


Post a picture of yourself with your GPSr at the coordinates with the directional guide post in front of you and Monks Mound in the background, 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 Birdman and how old is it?
2) What type of stone is the Birdman made of?
3) What is the name of the tributary that the mound builders used to access the Mississippi River and establish an extensive trade route?
4) Where did the mound builders get their soil to build these massive mounds of earth?
5) Cahokia discoidals are usually made of colorful quartzite and some are made of granite; what were they used for?

Additional Hints (Decrypt)

Lbh jvyy abg jnag gb zvff ivfvgvat guvf Jbeyq Pynff Vagrecergvir Pragre, fb gel gb fpurqhyr lbhe ivfvg qhevat gurve ubhef bs bcrengvba; vg vf zber guna jbegu gur fhttrfgrq qbangvba srr.

Decryption Key


(letter above equals below, and vice versa)



559 Logged Visits

Found it 549     Didn't find it 1     Write note 8     Publish Listing 1     

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Current Time:
Last Updated: on 11/21/2017 9:45:13 AM (UTC-08:00) Pacific Time (US & Canada) (5:45 PM GMT)
Rendered From:Unknown
Coordinates are in the WGS84 datum

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