The Park Police have been around a very long time too — at least since the late 70s/early 1980s in some of the urban parks. Regular NPS park rangers started going to “cop shops” and getting their law enforcement commissions back then too. Unfortunately, too many of them were wanna-be cops who could never make it in the big city. And, their attitudes have become more and more hateful-toward-park-visitors. Don’t get me started on my stories.
Park Police have been around for a long time as you say, but they were always a separate entity from your basic “park ranger”. Now, they are all vested with police power and I don’t believe that was the case until the patriot act.