Otto;John's got it about right. The tracks were NOT ripped up from Portland,but from Westbrook to Windham. The Amtrak station is on the first mile of the Mountain Div(which Guilford calls the Cumberland Mills Running Track). The "Mountain" leaves the mainline at CPF 196(just about where the long gone Portland Union Station was). Guilford freights run past the station to serve several consignees in the western part of Portland and Westbrook(Cumberland Mills is a part of Westbrook,the sight of a SAPPI paper mill,that gets/gives very few cars). From just past the mill tracks,the tracks were recently removed by Guilford.
Guilford kept this section,as far as S. Windham,and still owns the ROW. From S. Windham to the N.H. border,the state owns it,and a hiking,biking,and snowmobile trail,has been built this year,ALONGSIDE the existing tracks,just west of S. Windham.
Labor Day,1983,is considered the official end of the Mountain Div. as this is when through freights RY-1 and YR-1 (Rigby Yard in S. Portland to/from St. Johnsbury,Vt. made their last through runs. Guilford ran locals as far as Fryeburg/N.Conway to serve a couple of propane,feed and lumber firms sporadically for a year or so. There were also special moves including an "Operation Lifesaver Train" around 85'
While "scenic" and a railfans delight,Guilford saw the excessive cost of the Mountain,and began its interchange with the CP,at Keag,in Maine,not St.J.
While some railfans think there is "potential for freight service",there were few local customers,past Westbrook.(the papermill,in Gilman Vt. served from the St. J. end.)
The state has brushcut most sections of the line from the NH line back towards Portland,and "speeders" have traversed it.
The Fryeburg station was NOT in the center of town,but its site(and the site of former rail served industries,including a quarry,is reached by heading back to Portland a short distance,then taking a side road(the pond you mentioned is on the other side of Rts. 5 / 113. Not much to see!