1931 & 36 WMG
This excerpt from the the 1936 WMG may or may not help:
"Flat Mountain Ponds
The three ponds (2,311 ft) are connected by a narrow stream. They lie 2 1/2m. SW of Mt. Whiteface, between the two low summits of Flat Mt. One rounded summit (2,940ft) is SE of the ponds. The N summit (3,300 ft) is 2m. W. The chief charm of this region was the fine virgin forest, but lumbering began in 1920, and an extensive fire in 1923 completed its desolation.
The ponds may be reached by ascending the abandoned Beebe River Lumber RR to the NE either from Sandwich Notch road (see Squam map), or from the Bennett Street trail (see below). It passes along the NW side of both ponds, one branch diverging towards Lost Pass, the other continuing towards the Sleeper Ridge.
I will try and scan the 1931 waterville sheet and post it here.
Chris