Nice shot of this gully. When I got a good look at it a few weeks ago I was instantly persuaded that it was not formed by water erosion (too narrow and steep, and doesn't drain anything above it), but is some kind of seismic or volcanic crack. Did you notice any differences between the rocks on the two sides?
It looked like typical map lichen covered presidential range either granite or gniess. Maybe it's volcanic though. Probably would have to go in the summer to check the rocks in the actual gully that are covered in the winter. If it was a volcanic intrusion the rock in the gully would be different and the two sides would be the same. At least that is what I have observed on other cliffs (wiessner's dike on Cannon cliff for instance).