This Waymark falls within Chesapeake &
Ohio Canal NHP (Maryland), Entrance to the park is 5 dollars per
car including a 3 day pass.
Geology of the Island and Great Falls:
The geologic history of the falls is an interesting one. After the
last ice age, the ocean levels dropped forcing the Potomac river to
carve deeper in its path to the sea. The overlying rock was eroded
away exposing a much harder, resistant rock formation called the
Piedmont which is what Olmsted island consist of. This hard layer
is principally made up of highly metamorphic and igneous rock, and
may be seen throughout the island. For thousands of years the
Potomac river has eroded the bedrock, causing the falls to recede
upstream from a point 9 miles downstream near Chain Bridge to its
current position at Great Falls. Joint fault plains, natural
fissures in the rock substrata where shifting has occurred, exist
in many places in the Piedmont Formation between Chain Bridge and
the Great Falls. These areas of faulting have loosened the rock,
forming areas of weakness. The force of the river has eroded along
these areas changing the river's course to its current position. As
one walks along the pathway to the overlook, evidence of the
ancient river beds can be seen in well-rounded boulders, smoothed
surfaces and grooves, and beautifully formed potholes which were
once formed on the ancient riverbed. The metamorphic rocks provide
jagged rocky surfaces and high-walled cliffs, stark and pristine
against the crashing waters of the Potomac at the falls and along
nearby Mather Gorge.
To Claim this cache: find the answer the
questions below along the walkway and of course take a photo of you
and your GPS. If you log it you must be in a photo!
1. What did the Ancestral Annual Floods
provide?
2. About how long is the flood cycle?
3. Who benifits from seasonal pools?
4. How far did the sea level fall?
5. What is the date at the bottom of the plaque?
6. What makes the cliff faces colorful in the warm
seasons?
This cache is also 100% Handicap
accessible.
Geology Map of the Great Falls region
