A friend who works for a shortline railroad has a son who is an Amtrak locomotive engineer. One or two years ago, he told me they moved some equipment to or from that wye, and they were accompanied by an Amtrak police officer. I guess that walking to the tail end of that wye track was considered a personal security risk, as it looks like an inviting place for the homeless to congregate.
Since the tail of the wye ends in a rock cut, then I suspect that tail track never connected to anything; that is, it did not lead to/from some other location.
I know that Penn Central / Conrail had yard tracks at street level on the west side of Manhattan, somewhere around 32nd Street and Tenth or Eleventh Avenue, until the early 1980s. I know because several privately owned passenger cars were stored there at that time, and an AAPRCO meeting was hosted onboard the cars back in those days. Those surface yard tracks must have been connected to the West Side Line at another location, north of the High Line, because they had no connection to Penn Station trackage.