The Devon and Tremont Mines got their start in the mid-1800s before quickly merging.  They're near enough to each other that figuring out which trench or rock pile you're looking at is kinda difficult unless you've got accurate maps.  Or, more likely, you find the note written on a tree marking the Devon adit or shaft.  There's nothing open at either of these two remote locations so don't get your hopes up.  It's mostly just deep trenches criss crossing the forest and a few rock piles.  

Unlike a lot of mines in the Trap Hills, the Devon & Tremont Mines are relatively easy to find because the North Country Trail passes right by them.  If you know what to look for the trenches are just feet off the trail!