Another odd thing, I found what felt like part of a plastic lid as in for a coffee cup, this should not even have soon up unless some form of metal is used when making it, I thought odd, either way junk and thrown in trash.
Highland Park floods really bad, like up to the roof of the concession stand by the playground. So quite a bit of junk gets washed in. It was and still is to some extent used a lot for family reunions. I have been there many times for such events. It literally has tons of bottle tops, pull tabs and foil. They have also added a lot of wiring for Christmas displays. You have done well to sift those coins out.....G