Look a bit strange don't they. There may be nothing that links these sites and carvings. Visit any castle in Britain and you'll find evidence that someone got bored and did a bit or carving in the stone blocks. Even some of the towers of the Great Wall of China have been decorated with carvings. As these carvings are easily accessible it shows they aren't being hidden and could be easily placed.
The symbols are a right mix aren't they. Some have been adopted by wicca and there is the Ying/Yang, Anhk etc. The Swastika is a symbol that far pre-dates the Nazi's and how these are carved it is more like the positive symbol from India and Asia.
There are members of many cultures that moved to America, including a large Chinese population who worked on the railroads. I think the first question is when were they carved. Maybe the area's were quarried and they are labourer's marks or perhaps scouts have camped there and done some carving? I have been meaning to put some articles on symbology on the site, might be a good idea.