Certain of these trails are accessible from the City via public transport.
If you’re going to make the trip, I suggest heading to the Rockies, via Metro North. I describe how to do that HERE. It is quite a nice trip right along the Hudson.
Using MetroNorth’s Hudson line can also take you to the OCA Central section, which runs from Yonkers to just south of Tarrytown, and also paralleling the Hudson, just a few hundred yards inland. Just take a look at this map, which is set at Hastings-on-Hudson, and zoom out to the other stations along the Hudson Line, and see how close they are to the OCA itself.