Right, so this is actually less mysterious than you'd think - black squirrels are a melanistic variant of the eastern grey squirrel (Sciurus carolinensis) and they're genuinely not that rare along certain stretches of the Appalachians. There are established populations in parts of Pennsylvania and Virginia particularly.
That said, three in one week along the same trail section is worth noting. Melanistic colouration tends to cluster geographically because it's a recessive trait - you get localised pockets where it dominates the population. So you may have stumbled through a known hotspot without realising it.
What I'd want to know:
Exact location on the trail - which section, which state?, Were they interacting with grey squirrels or keeping to themselves?, Any unusual behaviour, or just... squirrels being squirrels?
I'm not going to entertain the ". Black squirrels are something else entirely". Crowd unless you've got something more compelling than colour. Melanistic animals turn up across dozens of species - black foxes, black deer, black rabbits. It's documented biology, not cryptozoology.
However - and I'll grant this - if you're consistently seeing them in an area where they simply shouldn't have a population, that's a legitimate distributional mystery worth logging. Has anyone cross-referenced these sightings with iNaturalist records for that corridor?
