Overview
The Kansas River flows along the south edge of an area that is
referred to by geologists as the "dissected till plains." The
Kansan glacier covered the nearby plains several hundred thousand
years ago and left behind an assortment of sediments. Land forms
deposited by glaciers such as drumlins, eskers, and moraines,
similar to the ones that are found in the upper Midwest and the
northeastern states, were formed here as well during more recent
glacial periods. The features found in other places in the Midwest
are not present in this region, since erosion during the long
period of time since glaciation has destroyed those "typical"
distinctive landforms. Glacial deposits occur with inconsistence in
this entire area of Kansas. As a result, the features of the region
are determined more by the underlying bedrock and its structure.
The bedrocks in this part of Kansas are 270 to 300 million years
old, dating back to the Late Pennsylvanian and Early Permian
periods of geologic history. They are typically a sequence of
alternating shales and limestones that were deposited in shallow
seas that covered the central United States during those
periods.
Paleozoic Bedrock
The Paleozoic-age bedrock as mentioned above was
largely deposited in a shallow sea in which the depth of sea water
was constantly changing. This changing depth of sea water resulted
in different types of sediments being deposited. These types are
represented by the different rock that we can see in the bluffs.
Generally, limestones were deposited in deeper waters, while shales
were deposited in shallow water. At times during the retreat of
these ancient seas, this area was at or slightly above sea level,
and shales, silts, and sandstones were deposited in river
delta-like coastal environments. Some of these areas supported lush
stands of swampy vegetation during Pennsylvanian time that were
later buried and converted to thin coal deposits. Many years of
geologic mapping and stratigraphic studies have resulted in the
recognition and naming of roughly 160 types bedrock in and along
the Kansas River valley from Kansas City to Junction City. These
individual rock units are often lumped together as members of
larger stratigraphic units called formations. These formations each
have a geographic name designating the area where they were first
found and recorded.
The Paleozoic bedrock was deposited during a time that includes the
latter part of the Pennsylvanian Period and the early part of the
Permian Period, a time span of 270 to 300 million years ago. The
contact between these two periods have no major interruption in
sedimentary deposits during this time period (this is defined as
"conformable"). Geologic formations are further lumped together in
named groups. The downward cutting of the Kansas River west to east
and the westward dip of the bedrock combined to make an outcrop
pattern of irregular north-south bands of similar rocks.
Within the immediate area of this Earthcache, two bedrock groups
can be found, and the following offers a description of each group,
hilighting the visible layers that can be seen from the
Interstate.
Chase Group
A signature of this group in this part of Kansas is a
solid and think base limestone that is gray to tan in color. It is
a dense type of limestone and sometimes is found with with some
small layers of gray shale. This limestone type averages 45 feet
thick.
Council Grove Group
A signature of the Council Grove Group in this part
of Kansas is a limetone bedrock that is a solid 330 feet of gray
limestone interbedded with gray, and distinctive red and green
shales. Generally these limestones are less dense and are made of
very thin, or small, layers than the overlying Chase Group.
Logging requirements:
Send the cache owner a note (click on "A Cache by Jeep_Dog" link)
with :
- The text "Kansas River Bluffs" on the first line and number of
people in your group.
- A description of the color and thickness of the rock you
observe at the top of the bluff.
- Using the group descriptions above, which group (Chase or
Council Grove) you determine the bedrock in this bluff to be
in.
- Request, but not a requirement (and can be helpful if any
answers for above question are incorrect): for additional
verification to avoid armchair logs, please include with your
online log a photo of your group with GPS at the cache
location.
The above information was compiled from the following
sources:
Beck, V. H., 1959, Geology and ground-water
resources of the Kansas River valley, between Wamego and Topeka
vicinity: Kansas Geological Survey, Bulletin 135, 88 p.
Fader, S. W., 1974, Ground water in the Kansas River valley,
Junction City to Kansas City, Kansas: Kansas Geological Survey,
Bulletin 206, pt. 2, 12 p.
Frye, J. C. and Leonard, A. B., 1952, Pleistocene geology of
Kansas: Kansas Geological Survey, Bulletin 99, 230 p.
Jewett, J. M., 1941, The geology of Riley and Geary
counties: Kansas Geological Survey, Bulletin 139, 164 p.
Mudge, M. R., and Burton, R. H., 1959, Geology of Wabaunsee
County, Kansas: U.S. Geological Survey, Bulletin 1068, 210 p.
Schoewe, W. H., 1949, The geography of Kansas, Part
2--Physical geography: Kansas Academy of Science, Transactions, v.
52, no. 3, p. 261-333
Zeller, D. E. (ed.), 1968, The stratigraphic succession in
Kansas: Kansas Geological Survey, Bulletin 189, 81 p.