A SCREEming Good Time!! EarthCache
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This Earthcache is located on the Tom Mays Unit of Franklin
Mountains State Park. Entrance fee is $4. Weekend visitors please
pay at the ranger station along the entrance road into the park.
Weekday visitors must use one of the fee honor boxes located at
either the entrance gate or the ranger station noted above (the
station will be closed but the box is located adjacent to the
building).
This Earthache is accessed by taking either the W Cottonwood
Spring/Mundy's Gap trail (shorter route) or the Agave Loop trail.
The specific location is along the Agave Loop trail very near its
eastern intersection with the W Cottonwood Springs trail. A map of
the park (including trailheads) is available
HERE for reference, although the above mentioned
intersection is not illustrated. Once at the trailhead, follow your
GPSr to the coordinates listed above.
THIS EARTHCACHE
Talus (pronounced, TAY-lus), or Scree as it is sometimes referred,
is defined by Spearing (1991) as a pile of rock fragments lying
below a cliff, which were derived from the physical and mass
weathering of the cliff face. Typically talus lies along a steep
slope as in the example shown below, and in the one you are
visiting here today in the Franklin Mountains.
Photo showing a typical talus slope, or scree field, below a cliff
face.
Photo by Kevin
Lenz, used in accordance with the creative commons liscensing
program.
The formation of talus is often attributed to the expansion of
frozen water in joints and irregularities of the cliff's rocky
face. During the day water may flow into these small cracks where
at night it later freezes when the temperatures drop. Water may
expand as much as nine percent when frozen, thus acting like a
wedge on the surrounding rock. As the rocks sluff off they fall to
form talus slopes below the cliff face.
ANGLE OF REPOSE
The angle at which the talus is resting is referred to as the angle
of repose. When granular material is poured onto a flat surface, a
pile will form that is roughly conical in shape. The internal angle
between the flat surface and the surface of the pile is known as
the angle of repose. Many factors can affect the angle of repose
including the density of the particles, surface area of the
particles, shape of the particles, and the material's coefficient
of friction. Material demonstrating a low angle of repose, such as
a pile of sugar on a tabletop forms flatter piles than material
with a high angle of repose, such as the rocks forming the talus
slope you are studying here today.
Illustration demonstrating the angle of repose of granular
material.
Illustration by Davius,
used in accordance with the creative commons liscensing
program.
TALUS WALK
If you took the W Cottonwood Springs trail up to this Earthcache
then you probably noticed that certain areas of the trail were very
rocky and a bit treacherous to walk on (This is where the 3 terrain
rating comes from!). These sections were actually a portion of a
talus slope that were incorporated into the trail. In some areas
the rocks move under your weight and sound like metallic ice
cracking beneath your feet! While areas like this may be tough to
traverse for us humans, they make excellent hiding and basking
areas for reptiles and other small critters. Keep your eyes open
for desert critters when visiting this Earthcache and don't forget
to bring your camera for some souvenir snapshots!
Here in the Franklin Mountains, small animals such as this lizard
utilize scree for protection
and access to heat or shade for their metabolic
thermoregulation.
Photo copyright © 2011 Broken
Trowel.
LOGGING THIS EARTHCACHE
In order to log this Earthcache, EMAIL ME with the answers to
the following questions.
- How tall would you estimate this talus slope to be when
standing at the posted coordinates?
- How wide is the talus slope at the posted coordinates where it
meets and crosses the Agave Loop trail?
- What is the approximate angle of repose at which this talus
slope is currently resting?
You do not have to wait on my approval to log this cache, however,
failure to provide the answers in a timely manner (no more than 24
hours) will result in your log being deleted.
REFERENCES
- Spearing, Darwin. 1991. Roadside Geology of Texas. Mountain
Press Publishing Company, Missoula, Montana. 418 pp.
- Wikipedia. 2011. Online article:
http://en.wikipedia.org/wiki/Scree
Additional Hints
(No hints available.)