Visited it on Monday. Had some work to do in the area, so I stayed in the beautiful Budget Inn in Mahopac. An experience not to be missed. On the plus side, the Put runs right behind it, so if you're planning to ride the rail-trail, it's actually a reasonable place to stay.
I found the railbed heading out of Yorktown Heights. It's now a fiber-optic cable right-of-way. Probably still owned by the park commission. It's quite walkable as far as I could see, but is overgrown at Baldwin Road on both sides. Goes through a cut and a fill -- it's quite obvious. On the west side of Baldwin it goes through a low cut, then fill, then a deep cut, then levels off as it comes to Mohansic Avenue East. It *sure* looks like it continues SW along Mohansic Avenue East, but clearly stops at Baldwin Road where there is a sharp incline. Don't know where they were going with that, and it's not on the property map Otto found.
The three maps that Otto linked to above disagree with each other. The 1910 map shows two branches, neither of them crossing the tail of Crom Pond. I can only find one on the aerial photos, and saw no evidence of a second branch (but neither did I go traipsing through the woods where it might have gone). The 1930 plat map seems much more accurately surveyed and reflects the physical evidence available to us.
On the north side of Crom Pond, in FDR park, the road that curves around between the lake and the pond is *certain* to be the railbed. At the bottom of its curvature, if you continue to walk as if it didn't curve, well, it doesn't. It continues out towards the pond until it got to wet for me to continue. Definitely a railbed, with drainage ditches and everything.
This service road continues to a T intersection. Continuing past this intersection with the loop road around the park is another obvious railroad embankment being used as a foot path. It got too muddy for me to continue, but I saw no reason for it to stop where I stopped. Snow was still melting. The USGS Topo map shows the rout north to 202 \as practically level. My speculation, which will require further examination when it ain't so fricking muddy, is that the center road inside the park is built on the right-of-way. It possibly continued to the north and could be where Fred saw it crossing.
It's unlikely that the eastern side of the loop road was the railbed, because it has a bit of a hill to it, and is too high up on the hill to have connected with a trestle over Crom Pond.