There is a trail map available online. Much of the trails are doubletrack that has been really ripped up by dirtbikes but there are nice sections of singletrack to be had. The singletrack wasn't built by mountain bikers so it tends to be very steep and sometimes unrideable in places.
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After parking in the lot across from the Brimfield State Forest garage ride Dearth Hill Rd where it begins to be unpaved and pay attention for doubletrack trails. Many of these lead to some short sections of nice New England singletrack.