GC2CAB2 Little Grand Canyon (Earthcache) in Illinois, United States created by WifeyB14

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GC2CAB2 ▼

A cache by WifeyB14 Message this owner

Hidden : 8/2/2010

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Size: Size: not chosen (not chosen)

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Geocache Description:

Wonderful area in Southern Illinois close to wine country. Part of Shawnee National Forest.

Little Grand Canyon – Murphysboro, IL

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Please answer the following questions at the earth cache coordinates:

1. How tall is the rock face at this point?

2. Does the rock face appear smooth or jagged? What color are the rocks?

3. There are 8 different depositional features you might find at this site. Some are easier to spot than others. Using the information, provide me 2 examples of what you see.

4. Besides mosquitoes, do you see any other wildlife in this area?

5. Is water present?

6. Is the vegetation flourishing?

NOTE: While it is NOT mandatory, I request you post a picture of yourself &/or your GPS at these coordinates so others can enjoy your adventure.

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A LITTLE BIT ABOUT THE CANYON:
Over time, erosion has carved this deep box canyon exposing its majestic bluffs. The stream that flows through the canyon travels about one mile and drops 350 feet from the ridge top to the Big Muddy River. This stream is what remains of the powerful waters that carved these ridges and valleys for thousands of years. A cool and lush bottomland habitat thrives on the canyon floor. Along the upper portions of the trail, visitors encounter expansive views of the colorful cliffs, the Big Muddy River and the Mississippi River floodplain. The canyon floor showcases seasonal waterfalls, large sandstone overhangs and towering beech and sycamore trees. The Little Grand Canyon has been designated a National Natural Landmark due to its unique ecological and geological features.

The site of the earth cache is at the bottom of the canyon, off the North starting point. If the rains have not been too bad, you can continue on to complete a loop. This 2.8-mile loop descends toward the edge of the Grand Canyon—a 0.75-mile river-carved, sandstone slot in Illinois’ Shawnee National Forest. The hike starts on a paved path, but after passing the observation platform near mile 0.4, the route turns sharply downhill into a sandstone slot on the canyon’s south side. Steps are carved directly into the soft rock: Take your time on and place your feet carefully to avoid slipping on the moss-covered surfaces. Stay alert and stick to the trail to lessen the risks. This area is also prone to flash flooding, so pay attention to forecasts pre-hike. Be sure to follow the white diamonds on the trees to stay on the correct path.

WHAT IS SO SPECIAL ABOUT SOUTHERN ILLINOIS, AND THIS AREA?
Most people think of Illinois, they usually associate our state with rolling corn fields. Most wouldn't believe that much of southern Illinois is far more topographically a part of the Ozark highlands of southern Missouri and northern Arkansas.

During the United State's last glacial period, around 20,000 years ago, a massive glacier known as the Laurentide Ice Sheet continually moved up and down, expanding and retracting, through what would become the State of Illinois. The grinding effects of the glacier left most of the Midwest, including nearly all of Illinois, as flat as a pancake. The glacier stretched as far south as St. Louis, MO, leaving everything to the north flat, while everything to the south remained untouched and geologically intact.

All of that water that melted off of the glacier during its periods of expansion and recession carved some remarkable geological features in the sandstone bedrock, leaving behind enormous canyons, cliff faces, and bizarre rock formations, many of which have been designated as National Natural Landmarks.
View Source: (visit link)

HOW IS A CANYON FORMED?
A canyon is a deep cut in the earth with steep sides and a relatively small bottom. While canyons can be massive in size, the size of the canyon bottom is generally extremely small when compared to the height of the sides. When compared to what's typically called a "ravine," canyons are typically much deeper and difficult to access. A canyon is a steep gorge with high sides and a minimal valley floor. While some consider a canyon to be a formation equal to a valley, the two aren't actually interchangeable. Canyons are significantly steeper than valleys. One of the most noted canyons in the world is the Grand Canyon in the United States.

Much like valleys, canyons are generally formed strictly through erosion. Typically formed by rivers, a few are also caused by massive movement of the Earth's tectonic plates. The two canyon types are similar, but do differ in their general form. Typically, a canyon forms when a river's course begins eating away at the underlying rock strata. As the water flows, it carries away much of the material making up the canyon's floor. As the water continues along its course, the canyon becomes deeper and deeper. The further the canyon progresses and the deeper it gets, the faster the erosion process becomes. The reason for this is that the canyon walls begin acting as a sluice, channeling the force of the water into a progressively smaller area.This is why canyons tend to be much wider at the top than they are at the bottom. The steeply sloping sides are caused by the water carrying dirt and rock away from the canyon walls, toward the far end of the river's course. As the canyon walls attain a greater surface area, they also pick up erosion from wind and rain, as well. As the canyon grows deeper, the exposed rock strata becomes more pronounced and the underlying geography of the area becomes visible.

The canyon walls are typically visible as layers of rock strata. Because the harder rock wears away significantly slower than the softer materials, the hard rock of the canyon walls is more readily visible along the canyon walls. Geologists study these rock strata to track geological events through the ages. These rock strata can assist geologists in tracking the progression of ice ages and other geological phenomena.

View Source: (visit link)

SANDSTONE CLIFFS:
Sandstone is defined as, “A sedimentary rock formed by the consolidation and compaction of sand and held together by a natural cement, such as silica.” Like sand, sandstone may be any color, but the most common colors are tan, brown, yellow, red, gray and white. Since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions.

In banking, “deposits” are something left behind for safekeeping. In TV police dramas a “deposition” is a witness’ statement; the heroes examine the statement for clues to solve the mystery. In geology, “depositional features” are clues in sedimentary rock left behind by wind or water that can make statements about ancient environments, telling us what it was like ages ago. Rock formations that are primarily composed of sandstone usually allow percolation of water and other fluids and are porous enough to store large quantities, making them valuable aquifers and petroleum reservoirs. Fine-grained aquifers, such as sandstones, are more apt to filter out pollutants from the surface than are rocks with cracks and crevices, such as limestone or other rocks fractured by seismic activity.

This sedimentary rock is prevalent to the canyon area and is widely visible to all the hikers in the area

To assist you with Question 3, here are examples of the 8 different depositional features you might find at this site.

___ Ripple marks. These are probably the easiest to find. You’ve seen these in soft mud. How long does it take for mud or sand particles to stick together and become stone? While chemical sedimentary rock formation can take place in hours or days or weeks or years (think about crystals forming as salt water dries up or minerals collecting on the insides of household plumbing), clastic sedimentary rock formation takes long slow millennia as the particles gradually bind themselves together.

___ Massive and unstratified sandstone blocks. The Elgin Sandstone is a mixture of sandstone, shale, and siltstone. Most of the neighboring rock formations are limestone. While limestone can also occur in massive and unstratified deposits (big blocks with no apparent layering), limestone is a chemical sedimentary rock which usually occurs in marine environments. The limestone layers above and below the Elgin Sandstone tells us the ocean was here before the river, and returned afterwards.

___ Parallel-stratified bedding planes. Some of the sandstone deposits show distinct layers, although the layers do not break apart easily. The layers could indicate periods of time when the river put down sediments and then paused, put down some more sediments and paused again. We need more clues to know how many years it took to form each layer.
Geology is the job of assembling the evidence to tell the earth’s story. In Hawai’i we can see lava turning into igneous rock before our eyes. Since no one was around to see the Elgin Sandstone actually form, anyone’s story is valid, as long as it includes all the evidence. Earth scientists are constantly revising their stories as new discoveries provide more information about the earth’s history.

___ Cross bedding. The light has to be just right to spot this. Over the years, seasonal patterns result in layers of deposits, showing up in the sandstone as streaks or faint parallel ridges. Years of west winds might blow sand grains into a dune on the bank of the river. Then a change in the depositional environment happens. Perhaps the river cut a new channel. Maybe a hundred-year flood stripped away layers of sediments and then formed a blockage with them downstream to create a backwater. It could even be that the underlying rock tilted in a cataclysmic event like an earthquake. Maybe the wind began to blow mostly from the south, piling up sand grains from a new angle. For whatever reason, the newer sediments are laid down on top of the older sediments, in a different direction.

___ Pebble hollows. Look for holes in the sandstone where shale pebbles collected and formed. The more loosely cemented shale eroded away, leaving hollow places in the more tightly bound together sandstone.
Here is a mystery: did the shale pebbles form at the same time as the surrounding sandstone? Or did the shale fill in holes left by something else, and then wear away to leave the holes again? Or were the shale pebbles there on the river bottom already, and the sand came along and filled in all around them to encase them in sandstone? What do you think?

___ Discontinuous layers of deposits. Sections of a layer either got eroded away later, or never got put down in the first place. Imagine a single section of the river, for example. Deep pools could acquire significant layers of sand or mud, while an island sticking up out of the water between the pools might not gain any deposits at all during the same years.

___ Load casts. This is the depositional feature you won’t find in many other places, so this is the one you must include as one of your two photos. Load casts look like sandbags minus the burlap sacks, except instead of piling up, they pushed down into the sediments below. It is thought that they represent heavy blobs of deposits from a single event, like a catastrophic flood that carried a tremendous amount of sediment downstream and dumped it suddenly along the way

___ Shale and siltstone with carbonized organic deposits. Sedimentary rocks are always recycling back and forth, turning from sediments into stone, and then eroding back into tiny particles again. In fact, shale is an excellent soil-forming rock. The amount of carbonized organic deposits you find here probably used to be a lot of swamp vegetation: plants not likely to be found in an ocean. No specimens survived intact as identifiable fossilized species. They may have been well decomposed into the black ooze of a river delta, before being preserved as a mineral deposit. Now the material looks like thin black smears on the paler shale and siltstone.

Additional Hints (Decrypt)

Or fher gb sbyybj gur juvgr qvnzbaqf ba gur gerrf gb fgnl ba gur pbeerpg cngu.

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
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N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)

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Little Grand Canyon EarthCache

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