Late last summer I was traversing the west shore of the Quimper Peninsula on the shore of Discovery Bay along a reach lined with bedrock. The bedrock is mapped as Quimper Sandstone and includes remarkable nodules that seem to be a feature of the sandstones in Jefferson County (see here).
Nodule in Quimper Sandstone
The sandstone also has fossils along this shore reach
Perhaps due to the fossils I was looking at the base of the bluff carefully and saw this unexpected feature that warranted closer inspection.
I have made numerous inquiries and have thus far come up empty as to why this tunnel is located here. I did not go in very far as I had no torch. So its one of those mysteries that will have to wait another day to explore. From a minerals perspective there really would not be any reason I can think of to bore a tunnel into this rock formation.
I was near this site yesterday, but logistics and other work prevented a side trip.