the Wisconsin Dells Earthcache
In Wisconsin, United States
Size:  (not chosen)
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Access to the site can be gained by parking in the lot designated for fishing off Finnegan Ave. Once in the lot, follow the trail south down into the ravine. Take care not to slip in the leaves or trip on any tree roots.
The Wisconsin Dells Earthcache
The Dells of the Wisconsin River encompasses over 5 miles of Wisconsin River corridor with a spectacular gorge, cliffs, tributary canyons, and rock formations carved into Cambrian sandstone. The Dells is located in southern Wisconsin and is well known for its scenic beauty, in particular for its unique sandstone rock formations. The Dells got its name from the French term “dalles” which means “slab-like rock”. During the 1800s, the Dells became a popular tourist attraction and has since grown into a major resort area.
Approximately 510 million years ago, during the Cambrian Period, this area of Wisconsin was covered by a shallow sea. For about 80 million years the seas flowed back and forth over the land depositing sand on the sea bed. Over time, the sand kept building up until, eventually, it rose above the seas. The sand deposits ultimately became sandstone.
Sandstone is very common and perhaps the best known type of sedimentary rock. As the name implies, sandstone is comprised of sand. However, there are a few other things to consider. Sand is characterized by any grain that is 0.1 mm to 2.0 mm in size. Any smaller grain size and you have shale or siltstone, any larger and you have either a conglomerate or a breccia. The grains can be composed of individual crystals of various minerals such as quartz or feldspar or even be a sand sized fragment of another rock such as a granite or a slate. A magnifying glass is usually sufficient to distinguish the general composition of a sandstone. The roundness of the grains is also important in determining the amount of distance the sand has been tumbled before deposition or the closeness of the source to the final deposit. The lack of fine grains and mud in a sandstone indicates a relatively high energy environment of deposition such as the wave action on a beach, the wind sweeping across a sand dune field or the rush of a river current.
The grains are important to geologists and so are the minerals that cement them together. Sandstone cements can influence the durability, color, porosity and usefulness of the stone. Normal cementing agents include calcite, quartz (silica), clays and gypsum. Silica cemented sandstone is very durable and hard. Calcite cemented sandstone is subject to acidic dissolution and is more easily eroded. Clay and gypsum cements, which are soft minerals, tend to produce much softer sandstone and the sand can sometimes be rubbed off in a person's hands.
Sandstone's banding is due to layers of sand that are deposited with differing characteristics. Sandstone is formed in many deposits that are episodic in nature and the resulting layers can be very different from previous layers. Sometimes the sand is courser or finer than the previous layer and this difference causes the banding.
Iron oxides, manganese oxides and other impurities can cause bright and contrasting colors in sandstones. These colors are what give sandstone its unique character and ornamental desirability. The colors range from bright whites, reds, yellows, oranges and even purples and greens. Colored sandstone is usually intricately banded in multiple colors which enhance its aesthetic appeal.
During the last Ice Age, approximately 19,000 years ago, the Dells was at the extreme eastern margin of the continental glacier. However, the Dells itself was never covered by glacial ice sheets - it was part of the large Driftless Area that was bypassed by the ice. The melting of the glacier formed Glacial Lake Wisconsin, a lake about the size of Great Salt Lake in Utah and as deep as 150 feet (45 m). The lake was held back by an ice dam of the remaining glacier. The eventual bursting of the ice dam unleashed a catastrophic flood, dropping the lake's depth to 50 feet (15 m) and cutting deep, narrow gorges and unusual rock formations into the sandstone seen today.
Much of the area is now owned by the Wisconsin Department of Natural Resources and was designated a State Natural Area in 1994. These unique sandstone formations can be found in only three other areas in the world, Switzerland, Germany and parts of New York.
As you descend and get closer to the river, look around and you will see the outcroppings of the sandstone cliffs. When you reach the water’s edge, turn and look back towards the ravine. On your right you will see a tall sandtone cliff towering above you. This is one of the few easily accessable views of the Dell’s unusual stone formations. As you investigate the cliff, make note of the different strata, the variety in colors, and the numerous shelf-like protrusions that cover the face of the cliff.
To get credit for this earthcache, you must fulfill the following three requirements.
1. Explain what natural occurance formed the ravine you walked through to get to the riverbank.
2. At the base of the sandstone cliff, there is a reccessed area somewhat like the entrance to a cave. Taking into consideration how these sandstone formations were formed, how was this reccess created and why is it smooth while the rest of the cliff is more angular?
3. And finally, post a picture of your team or GPSr in front of the cave-like reccess.
(No hints available.)
Last Updated: on 9/28/2014 6:28:58 PM Pacific Daylight Time (1:28 AM GMT)
Coordinates are in the WGS84 datum