From looking at an old map that I have and from memory:
To pick up either of the trails that Dave is referring to you would need to travel West on the RR bed from Marty's towards Joes Pond.
The 2 trail is at junction #CA108 and goes down into Peacham and W Barnet.
To get to the 234 trail from Marty's continue west on the RR bed and the junction is #CA109. This is where Joe's pond store is and you go over the bridge to get to 234.
Hope this helps you!