I hope to keep going back and collect what I can. The park itself has been expanded in a few areas finally last year. I found some of the bottles and other items were laid against trees and think they are trying to clean the woods and may get rid of anything they find. Oddly enough, the older items are closer to the roads. It looked like they burnt much of the items they tossed back in the woods as I found a few piles of melted plastics mixed with rocks and gravel.
The beer bottles have been the oldest found so far. One site said the brewery was open from 1899 until 1919.
http://americanhistory.si.edu/collections/search/object/nmah_871504