A Sandstone Outcropping at Desoto
A
cache
by &wife
Hidden:
1/1/2009
Size:
 (Not chosen)
Difficulty: 
Terrain:
(1 is easiest, 5 is hardest)
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Located in Alabama's Desoto State
Park with permission; an Alabama State Parks Geocaching Permit
has been secured. This massive sandstone outcropping is along the
blue trail. This area is open from 7am until sundown.
To log this earthcache find, you must
fulfill the following requirements:
- In your log entry, upload a picture of
yourself and your GPSr at the listed coordinates,
with the crooked tree that appears to think it is keeping the
outcropping from sliding into the creek below as your
background.
- Email to me, via the profile link above, the
answers to the following questions:
1. How long (in
feet) is this sandstone outcropping? The trail parallels the
outcropping, so step it off. Here is a hint: It is more than 50
paces.
2. What is the height of the outcropping at its
highest point (in feet)?
3. In 30 words or more, describe
sandstone.
Any claimed finds without proper documentation within 48 hours will
be deleted without notice.
The Cumberland Plateau section is the southernmost section of the
Appalachian Plateaus province of the Appalachian Highlands Region.
It is recognized by its pattern of relief features and landforms
that differ significantly from those of adjacent sections. It
occupies about 15 percent of the state and occurs as a roughly
northeast-oriented rectangular area in central and northeastern
Alabama, encompassing mainly Jackson, DeKalb, Marshall, Blount,
Cullman, Winston, and Walker counties, and it continues into
northeastern Georgia and Tennessee. The Cumberland Plateau borders
the Highland Rim section to the north, and the Valley and Ridge
province to the southeast. The landscape consists of flat-topped
high-elevation plateaus separated by deep, steep-sided valleys. The
plateaus slope gently from the northeast to the southwest. The
highest elevations are above 1,500 feet in DeKalb and eastern
Madison counties, and the lowest elevations are about 200 feet,
near Holt Lock and Dam in Tuscaloosa County.
The landforms are the result of differential erosion of the
underlying Paleozoic rocks in the section, which range from
Cambrian to Pennsylvanian in age (approximately 550 to 290 million
years before the present). The most resistant rocks are sandstones
of various ages, and these are what form the ridges. Pennsylvanian
sandstones belonging to the Pottsville Formation underlie the major
plateaus. The valleys cut through softer shale, limestone, and
dolomite. Of these three, limestone is most easily weathered and
eroded, and thus the deepest valleys are floored in this rock type.
The Wills, Murphrees, and Sequatchie Valleys developed where the
presence of anticlines, which are up arch folds in rock layers,
exposed the more easily eroded rocks. The plateaus of Lookout
Mountain and Sand Mountain developed on down arches in rock layers
known as synclines.
The Lookout Mountain district lies to the east of Wills Valley and
stretches from the Georgia state border in DeKalb County to
Gadsden, in Etowah County. It continues through northwest Georgia
to Chattanooga, Tennessee. At less than 10 miles wide and under 50
miles long, Lookout Mountain is narrower and shorter than Sand
Mountain. The plateau tilts toward both the southwest and the
southeast. Elevations along its northwestern edge overlooking Wills
Valley decrease from about 1,800 feet above sea level at the
Alabama-Georgia line to about 900 feet at Gadsden. The southeastern
edge of the plateau is between 100 and 300 feet lower than the
northwest edge. Along most of its length, the interior of the
plateau sags between 100 to 200 feet below the southeastern edge.
In the Wills Valley below and west of the coordinates, the Maury
Formation (also widely known as Chattanooga Shale) makes the base
of the local geology. The Fort Payne Formation, consisting of very
light to light-olive-gray, thin to thick-bedded fine to
coarse-grained bioclastic pelmatozoan limestone (meaning it
contains abundant pelmatozoa, an invertebrate zoology term meaning
'tiny critter') containing abundant nodules, lenses and beds of
light to dark-grey chert is next in ascending order. It is followed
by Tuscumbia Limestone, light-gray partly oolitic (a small round
calcareous grain) limestone; very coarse bioclastic crinoidal
limestone (meaning it contains abundant crinoids, including the sea
lilies and feather stars, that are characterized by a cup-shaped
body, feathery radiating arms, and either a stalk or clawlike
structure with which they are able to attach to a surface, i.e.,
more 'tiny critters'); light-gray chert nodules and concretions are
locally abundant. Lookout Mountain is known more for its limestone
than its sandstone, due to the abundance of karst formations at the
lower levels. However, the Tuscumbia Limestone is capped by the
Pottsville Formation, light-gray thin to thick-bedded quartzose
sandstone and conglomerate containing interbedded dark-gray shale,
siltstone, and coal. It is mapped not only on Lookout Mountain, but
also on Blount and Chandler Mountains, and Sand Mountain in DeKalb
County, and on the mountains of Jackson, Marshall, and Madison
Counties north and west of the Tennessee River. The Pottsville
Formation sandstone is of the Pennsylvanian type. This strata
consists of sandstone, siltstone, claystone, conglomerates, and
numerous coal beds.
Wills Valley lies astride I-59 from Attalla, in Etowah County, to
the Alabama-Georgia border. The valley is about 70 miles long and
ranges in width from less than two miles in the southwest to about
six miles across in the northeast. North of Attalla, the
northeasterly-trending Big Ridge splits the district, separating
Big and Little Wills Creeks. Wills Valley joins Big Canoe Valley of
the Tennessee Valley and Ridge section along a line from the foot
of Chandler Mountain's northeastern escarpment through Attalla to
Gadsden, but this boundary is not well defined
topographically.
Enjoy your visit!
Sources:
º Encyclopedia of Alabama Cumberland Plateau Physiographic
Section
http://www.encyclopediaofalabama.org/face/Article.jsp?id=h-1301
(accessed: January 2, 2009).
º Pottsville Formation
http://tin.er.usgs.gov/geology/state/sgmc-unit.php?unit=ALPApv%3B3
(accessed: January 2, 2009).
º Tuscumbia Limestone and Fort Payne Chert
http://tin.er.usgs.gov/geology/state/sgmc-unit.php?unit=ALMtfp%3B3
(accessed: January 2, 2009).
º Geologic units in DeKalb County, Alabama
http://tin.er.usgs.gov/geology/state/fips-unit.php?code=f01049
(accessed: January 2, 2009).
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