This is at the trailhead to several beautiful short hikes in a small-town Wisconsin Park. I visited here initially to find a traditional cache, hidden nearby. This earthcache is located of of Hwy 42 in Fish Creek, WI.
History: In 1998 the Township of Gibraltar, along with a DNR Stewardship Grant, purchased this 27.9 acre parcel of of property from the Welcker estate, one of the community’s earliest families. Until 1998 the property was the sight of the Bonnie Brook Motel run by Fred Welcker. At the base of the steep hill, to the west of the creek, is the original sight of the Peninsula Players Theater.
The creek, Fish Creek, for which the village is named, runs the length of this property and approximately 15 acres of this natural area is designated wetlands. Wetlands, also known as swamps, bogs, or marshes, act as natural pollution filters, making many lakes and streams cleaner and drinking water safer. They act as ground water discaharge areas, retain flood waters and provide valuable and irreplaceable habitat for many plants and animals. In addition, they provide scenic open spaces. Half of Wisconsin’s original 10 million acres of wetlands have been lost and many of those remaining are degraded.
Geology: This area is geologically built upon the Niagra Escarpment, more specifically, the “bedrock” of the area is a stone called Dolostone. (see the nearby GC1YH3Y for more information about Dolostone).
In contrast, the LARGE stone in front of you is TOTALLY different. Because it is not a white “sandy” stone with fossils embedded in it (Dolostone), this granite boulder is 'erratic' at this location; that is, it was brought here by man or nature, and does not naturally occur at this location.
As you look at the large stone in front of you, you should notice that the rock is composed of minerals that you can see (a phaneritic texture is the scientific word). Thus it can be rightfully assumed that granite is an igneous rock. If you examined the rock, you can see it is a mixture of light and dark minerals. The phaneritic texture(the ability to see the individual crystals/minerals) reveals that the rock was cooled slowly, within the crust of the Earth. Together, this texture and the light color of the rock tell you that these rocks are probably granite.
Granite is light in color because it is composed largely of minerals that are rich in silica. These include quartz, feldspar (orthoclase and plagioclase), and muscovite (a mica). Quartz is milky white, feldspars are pink, white, or gray, and muscovite is silvery. The dark color of granite comes from dark colored minerals, including hornblende, augite, and biotite (another mica). These minerals are green, brown, and black in color.
Granites actually come in many different colors. This variety in granites is caused by differences in mineral composition, especially in the feldspars. If feldspars are potassium-rich (orthoclase) the granites may be tan to reddish in color. If feldspars are calcium-rich (plagioclase) light to dark gray colored.
Erratics: If an erratic is in a location because of geological action, it is likely left there because of some massive change in the earth – such as glacial retreat/melt where the ice that had been carrying the large rock(s) simply melted, leaving the rock in its wake. If this is the case, you often see several rocks in a region, all of similar type but differing from the bedrock in the area If an erratic is in a location because of human interaction, it is usually to meet functional or decorative purposes. It may adorn a park entrance, help hold out water or hold back dirt, or create landscaping elements. If this is the case the rocks are usually systematically arranged for visual effect or for functional functionality. Congrads to Peach107 for FTF.
Logging Requirements: Send the answers to #1-#4 to me through my geocaching profile.
1. List the name “GC 23G40 Glacial Erratic at Fish Creek Park Earthcache” in the first line of your email. Also, list the number of people in your group.
2. View the large rock in front of you. Based on the description, is this type of granite an orthoclase or plagioclase?
3. As you look around the park (and drove into the village) do you think that this rock was placed here by glaciers (as they retreated) or by man (to decorate the park)?
4. Granite has a mass/weight of 166.5 lbs per cubic foot. What is the approximate weight of this granite boulder? (Multiply length X width X height to get the number of cubic feet then multiply that # by the weight/cubic foot.)
5. Post a picture with your log of yourself and/or a personal item that shows the sign at the entrance to the park. DO NOT show the large stone in your picture or your log may be deleted.
I will only respond if you have incomplete logging requirements. Go ahead and log your cache
Resources:
Fish Creek Park brochure. Petrology of Ice – scienceblogs.com -- http://scienceblogs.com/greengabbro/2008/08/the_igneous_petrology_of_ice_c.php Mineralzone.com -- http://www.mineralszone.com/minerals/granite.html