You can park at the end of Bates Road and walk on the beaten up path through the woods to the right of the RR tracks to get to the power lines, and follow the Circuit Bay Trail to GZ or you can park in the Market Basket parking lot and walk across RT126 to the break in the guardrail and follow the Circuit Bay Trail, past Erratic Beast. Take Caution, there are sometimes dirt bikers that go around these trails.
FTF: Dickster1