This waymark falls within the Chesapeake and Ohio Canal National Historic Park. Entrance to the park only at Great Falls is 10 dollars per car including a 3 day pass. From the Great Falls entrance, the cache is 100% Handicap accessible.
Alternate free parking across from Old Angler's Inn on MacArthur Blvd. offers scenic walks along the towpath or along the Berma Road trail above the canal to the Falls overlook. It also offers access to the Aquarius virtual cache. On crowded days, a slightly longer walk from Carderock (accessed from Clara Barton Parkway) provides ample free parking just steps from the towpath. Either choice allows a detour via the rigorous Billy Goat trail with wonderful views of the gorge along the way.
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 consists 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 answers to the questions below along the walkway. We encourage you to post a traditional photo of yourself and your GPS at the site, but this is not required.
1. What did the Ancestral Annual Floods provide?
2. About how long is the flood cycle?
3. Along the walkway two environments with different oak species are described. Name the trees and describe how what they need is provided by the geological differences.
4. Describe the rock outcropping in the viewing platform (color, type of rock, etc.). Are the cracks vertical, horizontal, in sinuous curves? What features capture rainwater? Notice the lichens on horizontal rock surfaces to right of the platform; what has happened within the platform?
5. Who placed a plaque here honoring Frederick Law Olmstead Jr., son of the designer of Central Park in New York City, and why was the island named after him?
6. What did the Potomac River Valley at this point look like 2 million years ago?
7. How far did the sea level fall?
8. What makes the cliff faces colorful in the warm seasons?
9. Returning across the bridges, note that the railings can be removed. During Hurricane Agnes in 1972 and a flood in 1996, the force of water and logs piled up against fixed railings tore out the bridges. Now, when a flood threatens, the railings are removed, and flood waters and debris flow under and over the bridge decks. Why are visitors sometimes surprised when they lean against the railings?