Yep, almost certainly Norovirus. Super highly contagious and can only be killed on surfaces with bleach. It’s not the trails that are infected, but all the motels, hotels, restaurants and other public facilities along the trails that are harboring the disease, exacerbated by poor cleaning and sanitation practices.
Most likely, unless a concerted effort is made to properly cleanse all of the these facilities all at the same time, this nasty little disease is gonna hang around for a very long time.
Reminds me of that rash of cruise ships a couple years back that got dusted with the stuff.
All it takes is one person to not wash their hands after using the can, touches one surface, and it goes from there.
[See Muslim ‘custom’ of using a hand to wipe their butt.]