There is a ranger station on Wissahickon Avenue in Blue Bell Hill, which is a really beautiful small village in the city mostly surrounded by the Park, and the city employees there should be able to send you in the right direction. If they are unhelpful, ask for Tom Doyle, one of the rangers there; he might need to do some digging, but he can find out; he was born in a Park house, which sadly is now in ruins.