1700s iron furnaces in CT and NY:
Most of the forest in CT, MA, VT was cut down for charcoal to fuel industry in the 1700s. There are remnants of the 1700s steel industry:
Kent, CT, Kent furnace
http://www.ericsloane.com/museum.htm
Salisbury, CT: Mt. Riga blast furnace,
http://www.nynjctbotany.org/lgtofc/m...stfurnace.html
Copake, NY (~10 miles or less from AT and on the south Taconic trail) has an 1845 blast furnace,
Copake Iron Works,:
http://www.flickr.com/photos/itinera...n/photostream/
http://nysparks.com/parks/attachment...ndSchedule.pdf
If you know what to look for there are many small quarries in New England. I've come across these in Brattleboro VT and Worcester, MA. You'd have to talk to local historical societies to find these.
In New England there are many, many former factory buildings/mills from across the ages. The museum version would be the Lowell and Lawrence mills. Most of the towns near the AT in CT, MA, VT and NH would have these and most are abandoned or restored/renovated into something else. You could get in trouble (legal or injury) going into abandoned mills.
There are a lot of little local history museums in the Berkshires that can be interesting.