I was just thinking about (and probably looking at, if it's the same one) that slide last Thursday. Looking at some photos I took from the fire tower on Mount Adams, it looks like it's not on the main bulk of Marshall at all, but on the next peak south in the MacIntyre Range. I'm at work at the moment, so I can't be certain, but I think it may be on that 3600-foot peak. If not, it must be on the 3900-foot one, but that one doesn't look steep enough, going by the contours on my map here.
Winkler wrote about a trip to the slide in an old issue of "Adirondac," if that's any help. I read it one day at With Pipe & Book in Lake Placid. I'm afraid I have absolutely no idea the date of the issue, however.
Two more things about Marshall:
1) It sure looks from the viewpoint (behind the summit sign) that the southern end of the mountain is higher than the area of the viewpoint and the summit sign, and
2) Was I seeing things, or was that Couchsachraga I could make out over there?