Twin Rocks Earthcache EarthCache
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This is an Earth Cache which means there will not be a hidden container or logbook to sign. Instead, you will need to visit the posted coordinates, make some observations at the site, and e-mail the answers to several questions.
This earthcache takes you to an area known by the locals as “Twin Rocks” due to one of its unusual rock structures, two interesting rock pillars along the roadside. The road ditch is comprised of multiple rock formations making this a truly remarkable spot. The formations are especially visible when leaves are not on the surrounding trees and shrubs.
The rock formations in this area were created by ancient oceans followed by erosion from glacial ice flows and melt waters as explained below.
Formation of the bedrock:
The bedrock seen here originated as sediment on the floor of warm, shallow seas that covered the mid-continent about 420 million years ago during the Paleozoic Period. That environment is where organisms such as tiny shellfish and coral which develop calcium carbonate shells and skeletons can easily extract the needed ingredients from the water. When these animals die, their shells, skeletal remains, and algal and fecal debris accumulate as sediment that might be lithified into limestone. Limestones formed from this type of sediment are biological sedimentary rocks. Their biological origin is often revealed in the rock by the presence of fossils. These lime rich rocks (primarily dolomite, limestone, and sandstone) are of the Silurian age.
The glacial erosion (or lack thereof):
During the last period of glaciers, most of Iowa was under a layer of ice that would one day become vast prairie landscapes. Clayton County, and much of northeast Iowa, was spared the effects of this last glacial period. It is located in Iowa’s Driftless Area. The Driftless Area or Paleozoic Plateau is a region in the American Midwest noted mainly for its deeply carved river valleys. While primarily in southwest Wisconsin, it also includes areas of southeast Minnesota, northeast Iowa and northwest Illinois.
The term "driftless" indicates a lack of glacial drift, the material left behind by retreating continental glaciers. Overall, the region is characterized by an eroded-down plateau with bedrock overlain by varying thicknesses of loess, or fine-grained, silty, pale yellow or buff, windblown (aeolian) sediment.
The post-glacial erosion:
In Iowa, Pre-Illinoian age till (unsorted glacial sediment deposited more than 300,000 years ago) was probably removed by natural means prior to the deposition of a thin mantle of colluviums or loess. As a result, bedrock is often exposed or is very near the surface in this area. At the end of the ice age, abundant melt waters from receding glaciers carved deep valleys in this rock resulting in the exposure observed in the area of Twin Rocks.
To log a “find” on this Earthcache, you must complete the following requirements:
1. Visit the rock formation at the posted coordinates, and
2. Send an e-mail to the cache owner containing answers to the following questions:
a) Estimate the total height of the rock formation at the posted coordinates,
b) Give the elevation (read from your GPSr) at the base of the formation,
c) Give the direction that the surface of the rock formation is facing,
d) Describe the texture and color of the rock surface (look closely as lichen of various colors often grow on the surface masking the rocks’ true color), and
e) Describe the business that had operated just east of the formation (at additional waymark QE) and explain how it pertains to this area.
Any "found" logs not meeting these requirements will be deleted.
PLEASE DO NOT POST ANSWERS IN YOUR ON-LINE LOGS!
Although not a requirement, feel free to post a picture of yourself with the rock formations.
Driving directions: You will need to take gravel road B60 (a.k.a. Eagle Ave. and Farmersburg Rd.) from either nearby Farmersburg or the Gunder Road (a.k.a. Co. Hwy X16). Please park safely on the road shoulder or at the additional coordinates provided while investigating this earthcache.
Additional Hints
(No hints available.)