Scotty is referring to the old line that ran through New Paltz itself and is now a railtrail. Not sure if you know it existed, since you asked about the West Shore. When you leave Mohonk, you will cross it at the east end of the Rte 299 bridge over the Wallkill River. The old station is on the north side and is now a restaurant. This branch ran down the Wallkill River valley from Kingston and met with the Erie's branch running up from Goshen, passing through Campbell Hall, running just west of Maybrook Yard and up to Montgomery. (I believe Montgomery is where the track officially changed owners- Erie south, NYC north.)
I'm not sure if the West Shore was too far away for a Mohonk "shuttle," though I am sure some patrons arrived that way. There also was a trolley between Highland and New Paltz at one time.
A side note: when you drop back down the mountain, turn right on 299. Just up the road, 299 bends left and a secondary road continues straight to a stone gatehouse. That was the original entrance to the property, with a private carriage road all the way up. Continue on 299, turn right at the crest of the slight hill onto Butterville Rd, and you will cross under a bridge from the old carriage road.