John Smith's posting had a comment that had a Flickr link of a stone arch bridge that is part of the original Galena & Chicago Union construction. Construction started on the G&CU in Chicago in 1852 and this bridge was built in 1865. (I'm guessing they had a wood trestle before that.) A 2013 Google Photo shows the trail under it was still in good shape. A June 2016 photo shows the trail is closed under the bridge. And an Aug 2016 photo shows how nature has taken over. Bridge Hunter indicates a creek flood took out the trail on the other side of the bridge.