Great River Road EarthCache
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At this location you will find several interpretive signs
describing the geology, flora and fauna of this region. Review
these signs to answer the questions below. Note that due to the
number of signs and amount of text to read through, that I have
upped the difficulty on this Earthcache a little bit.
From Winona to La Crosse, the Mississippi River valley displays its
greatest depth as it extends vertically through the sedimentary
rock plateau. Here, Highway 61 follows the narrow strip between the
river and the steep bluffs that mark the valley's western wall. The
valley walls are composed of two different types of rock, which
formed about 500 million years ago in a warm, shallow sea that
covered much of what is now North America. The lower, more sloping
parts of the valley walls are composed mostly of weakly cemented
sedimentary rock which erodes easily. On the upper parts of the
walls, steep cliffs shape the bluffs. The cliffs are composed of
dolostone, a chemically altered sedimentary rock that is resistant
to erosion.
Bluffs are formed as the Mississippi River or a tributary cuts into
the soft sedimentary rock, initiating rockfalls that undercut the
dolostone. The dolostone then breaks along vertical joints, leaving
steep cliffs. Two of the most prominent bluffs in the area, are
visible from this site on the west side of the valley. Both are
designated Scientific and Natural Areas by the MN DNR for their
unusual geology and rare biological communities.
These bluffs are within and area of deeply eroded stream valleys
primarily east of the Mississippi River and covering southwestern
Wisconsin. During the Ice Age of the last two million years,
glacial ice never passed over and leveled this area, and no drift,
or glacially carried sediment (clay, silt, sand, gravel and
boulders), was deposited here. However, the landscape before you
was blanketed with a layer of loess - a wind-blown, tan-colored
rock dust. This dust was carried by winds from floodplains still
bare of vegetation, which were repeatedly loaded with very fine
sediment by streams that drained melting glaciers. Today, a
distinctive and fertile soil has developed in the top of the loess,
which helps to give rise to the diverse and sometimes unique plant
communities found on these bluffs.
To log a find on this Earthcache email me the answers to the
following questions:
1) Approximately how many feet deep is the Missippi River
Valley along this stretch of Hwy 61.
2) What two types of rock predominately make up the bluffs and
valley walls in this area.
3) This area of MN and WI were not directly affected by the last
Ice Age. What name is used to describe such a region and how large
is this region?
4) Give a brief description of a "Goat" prairie, including a
specific measurement found on the interpretive signs.
5) What indirect glacial impacts did this region experience during
the last ice age?
6) What specific scenic landforms are visible from this
point and in which direction do they lie from GZ? Answers of
"bluffs", "Mississippi River", etc. will not be accepted.
7) (optional) Post a photo taken from GZ with your log, so everyone
can see how the area looks during different seasons. Feel free to
include members of your group if you wish, but avoid including
close-ups of the informational signs in your photo.
I apologize if the questions above seem overly specific or
difficult, but the intent is to prevent people from logging a find
who have not physically visited this site. If you visit the site
and read the available interpretive signs, you should have no
problems. If you are concerned about your answers, be sure to take
a photo of your group/GPSr as concrete evidence of your visit.
Additional Hints
(Decrypt)
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