Burrel

 

I'm sorry but I don't see how you determine Civil War vs 1840's or 1870's?  Like Sherlock Holmes advises: “It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.” – A Scandal in Bohemia 

There is a tree with 1859 carved on  it just outside where cave entry would be.  Something  caused the cave to be closed and seal.  The sink hole did not appear until years later.  Here is the picture of the tree.  It also has a map carved as well.

If you look to the lower left of the picture.  You can also enlarge the picture which helps.  It looks like a civil war Blacksmith bored a hole in the rock and mounted something in the hole.  I am thinking that there are lead shavings on top of the rock.

Sorry lower right side of picture