Colored Sands Earthcache
Location
Located at Colored Sands Forest Preserve in Winnebago County, Illinois, this earthcache will give an overview of the unique sands that were deposited in this area. The earthcache waypoint is a bit less than a mile hike from the parking area along a dirt (sometimes sandy) trail and overlooks the Sugar River.
How to log this cache
This is an earthcache so there is no physical container at the cache location. Earthcaches provide an earth science lesson and to log the cache as found, please answer the questions at the end of the description and email your answers to me, the cache owner, through my geocache profile page.
Geology
Starting approximately 25,000 years ago until about 13,800 years ago, during the last ice-age that geologists call the Wisconsin Glacial Episode, the edge of a continental glacier lay roughly 20 miles to the north of here. As the glacier melted, a torrent of water rushed down the Rock and Sugar River Valleys. These torrents carried great quantities of sand and gravel washed out from the melting ice.
The torrent of water rushing down the Sugar River valley was smaller in comparison to that of the Rock River Valley (yet much, much larger than the Sugar River you see today). As such, the size of the sediment the water carried were smaller, sand-sized sediments while larger gravel sediments were carried along the Rock River Valley. Consequently, vast deposits of sand were deposited along the Sugar River Valley in this area. After deposition, the prevailing westerly winds then picked up the sand and deposited dunes over the uplands on the east side of the Sugar River Valley. The predominance of sand along the river gave the "Sugar" River its name.
The sand that is deposited here from the glacier was originally part of a well-known sandstone called the St. Peter Sandstone. The St. Peter Sandstone was deposited 450 million years ago during the Ordovician period. At that time, Illinois was covered by a warm, shallow sea, and was located a little ways south of the equator (about 25 degrees south latitude).
The St. Peter Sandstone is typically composed of almost pure quartz (silica dioxide) grains. Locally, however, naturally occurring iron oxides and other minerals have “colored” the sand. According to local legend, many years ago, during the early 1900s, people from Rockford would travel to this area for picnics near the bridge over the Sugar River on Yale Bridge Road. There was a hill with layers of sands of different colors, green, orange, and yellow, and people collected the sands and put them in layers in jars for display. The road and bridge at that spot were moved long ago and the hill is covered in vegetation, so don’t bother searching for the colored sands now. However, walking on the trail to this location I did notice some subtle variations in sand color. Did you?
Questions to Answer
To claim a smiley for this cache, please answer the following questions and email me (the cache owner) through my geocaching profile page. Please include the name of the earthcache in your message.
1. About how many feet of sand are exposed at this location? Please do not go down the cliff to the bottom of the river here! We don't want to cause any more erosion. Just give it a good eyeball estimate.
2. Scoop up some sand from the trail and take a good look at it. If you have a magnifying glass or hand lens that would be most excellent to use! Describe what you see. What color is it? Do the sand grains vary in size or are they about the same? Is it a course, medium, or fine grained sand (or a combination)? Is there anything else interesting you'd like to note? Please do this observation in the field and don't remove any sand from the preserve.
3. On your hike back to the parking area or other parts of the park, pay attention to the subtle differences in sand color in/along the trail. How many different colors did you see and what were they? If you see any ant hills, what color of sand are the ants piling compared to the surface?
Enjoy the rest of your time at Colored Sands Forest Preserve. Feel free to post a picture of your group at this scenic overlook. This is, of course, optional.
Sources
Frankie, Wayne T., Dennis R Kolata, Richard C Berg. “Guide to the Geology of the Rock Cut State Park and Rockford Area, Winnebago County, Illinois.” Illinois State Geological Survey Field Trip Guidebook 1999-C.
Johnson, Lynda, “Into the Wild: Colored Sands Forest Preserve: Birds, wildflowers and geology!” The Rock River Times 5-11 May, 2010. Accessed online 2 July 2013.
Permission
Permission for this earthcache was granted by Winnebago Forest Preserve District on July 3, 2013.