Yah the bridge was destroyed by fire in 1904, it did carry people from both sides of the park, some of the supports can still be seen.
The Concord Conservation land had ball fields and a bicycle race track.
The State Reservation side had the swimming, swings, train station and, a dancing hall. If you walk along the tracks on the Pond Path you can see where the train station was if you look closely.
Working at Walden I always get scared everytime I hear that whistle blowing on the backside of the pond, people don't realize (or don't care) that the tracks are still active.
Thanks for your help guys and I'll look for some postcards.