Sara,
You are probably better off on Hobart rather than Beacon, but either works.
When you take the trail, right (and DOWN) from the stop light, you go into the woods, make a right (down) curve around and go down about a mile, then make a left over a bridge (steep, but short down).
You will curve past the lake. There is a mowed lawn between the lake and the tracks. Go towards the far left corner of this (past a pretty tree covered in poison ivy on the lawn). There is a pretty clear, DIY trail with a little bridge accross a drainage ditch and accross the tracks to the Junction Hollow bike path.
You'll have no problem, when you see it.
When in doubt, go downhill, you will get to the river.
Mick