MINI-PROBLEM: STONE MOUNTAIN MONADNOCK
Stone Mountain can be correctly called a monadnock, an inselberg, or an exfoliated dome. It is a
unique geographic feature, being 1.3 miles long, 0.6 miles wide, but an undetermined depth. There
are similar but smaller features in the area, like Arabia, Panola, and Pine Mountains. Rock similar to
Stone Mtn. is or has been exposed in the Piedmont province over the last 200 million years. The area
surrounding Stone Mountain is primarily composed of the Clairmont and Wahoo Creek Formations, a
biotite gneiss and a mica schist. We are going to explore this unusual feature up close and personal.
We will make several stops, the first several on the walk-up trail starting on the west end,
Confederate Hall museum, a few stops in the east quarry, and a final one near Stone Mountain Lake.
You and your team will investigate each stop in as much detail as time allows, take notes and make
sketches in your notebook, and hopefully have vigorous and meaningful discussions about what you
are observing and its hypothetical significance. Based on your current knowledge and the field data
collected at Stone Mountain, you and your team will write a logical response to each of the questions
posed in the conclusion. You can turn in the typed conclusion questions and your hypotheses at the
end of class tomorrow. One copy per team. Good luck and have fun.
West Walk-up Trail
Stop 1.
Look closely at one of the large slabs of Stone Mountain rock along the road in the west walk-up trail
parking lot or anywhere on the hike.
Identify the texture, mineral composition, crystal size, rock type, and rock name. Crushed samples of
this rock were tested with a mass spectrometer. The Ar-40/K-40 P/D ratio was measured to be 0.18.
Please do not walk anywhere except on solid Stone Mountain rock. Some solution pits have
rare and endangered plant species.
Stop 2.
Look for white bands that run through Stone Mountain. Especially look where two of these bands
cross like an X about 20 feet above the first big quarry ledge on the hike up to the flagpoles. Walk
around this area and find several of these bands. Follow a few of them along their lengths. Make
observations.
Stop 3.
The surface of Stone Mountain is covered with irregular, varying-sized depressions, called “solution
pits.” Investigate several of these empty depressions. Stone Mountain is obviously made up of a
unusually homogeneous rock with very few vertical fractures, or joints. Also consider that all of the
rocks we see in the “old” Appalachian Mountains are the cores of these mountains as several
kilometers of overburden rock have been weathered and eroded away downstream over millions of
years. Note the way Stone Mountain does seem to fracture. Consider the meaning of the word
exfoliation.
Stop 4.
Find and observe a few solution pits that have collected sediment.
Stop 5.
Find and observe a few sediment-filled solution pits that have very low, ground-hugging forms of life
in them.
Stop 6.
Find and observe a solution pit that has similar forms to 5 but also has a few more forms of life, but
nothing higher than 2 feet.
Stop 7.
Find another larger area that has one kind of tree and observe.
Stop 8.
As we walk up past the flagpoles, find a large area that has additional trees with broad leaves.
East Quarry
This area is an abandoned granite quarry on the east end of Stone Mountain. Mining ceased in 1970.
Stop 9.
In the extreme lower left part of the quarry, look for light parallel lines of minerals. These lines are
called flow banding.
Stop 10.
Find an irregularly-shaped block of darker material embedded in Stone Mountain rock. There are a
few of them about 1-2 feet in diameter. These blocks are called xenoliths.
Old Route 78
This stop is a few hundred yards north of the East Quarry. It is a 400 meter long old road that leads
east toward the shore of the lake.
Stop 11.
We will walk down a short road that runs E-W to the edge of the lake. Note the weathered white rock
and soil in the road cut. The rock is Stone Mountain rock. The weathered material is a mineral found
in abundance along the Fall Line. As we walk down the road, watch for a change in the color of the
soil from white to orange on both sides of the road. Notice the soil eventually changes back to white
a bit farther down the road. Find a piece of the rock in the orange (iron-rich) soil. The Ar-40/K-40 D/P
ratio in the rock is 0.13. Mr. Schafer will explain about how to make a simple geologic map of this
area in your notes.