There's a book about northern N.H.'s logging railroads, and it includes info. about the Sawyer's River. I'll check it out and post some of the info.
As for moose being dangerous: I live in moose country. Young moose (yearlings) are quite tame and somewhat approachable. They're more curious than anything else, and will let people come fairly near them (and, conversely, will come near people) without being fazed. Adults, however, are another story. Bull moose, during rutting season (mid-spring and mid-autumn), can be aggressive, as can cow moose when they're in heat or hanging out with their newborns. They can, and do, chase cars and people. As long as you stay your distance and quietly watch them, you're pretty safe. But if they perceive that you're a threat, you may find yourself in big trouble. If you're in a car, a moose may do a great deal more damage to the vehicle (and to you!) than it will do to itself. A large adult moose can weigh 1200 pounds --- and, contrary to appearances, it can run quickly and with agility.
