The End of the Trail (The Hardy Boys #162)

Hiking the Appalachian Trail with their friends, Chet, Phil, and Biff, the Hardys hit a snag when daredevil Biff gets hurt. The old mining town of Morgan's Quarry is the nearest place for help. But even the run-down, isolated town turns menacing when two tough locals drop a bag full of money in front of the brothers!
Joe and Frank are stonewalled when they ask about the money. The roads are washed out, the phones are down, and a crumbling mansion hides a gold mine of secrets. Every fork in the road leads to more danger...and everyone in Morgan's Quarry seems bent on makng sure the boys don't make it out alive!