A very good question...  At first glance it sounds like they could easily be trail markers, but probably not in that area of the park.  They're most likely Pheromone Bags (or traps) placed onto the White Bark Pines in the area in an attempt to kill the Beetles that are damaging that tree species.

If you're interested in learning more about this kind of beetle and/or the bags themselves, this blog entry actually seems to be right on point:

http://pointsoflight.blogspot.com/2008/07/meet-beetles.html

Let us know if anything else comes up that you're wondering about.