The map of Monson's quarry branches approved by the state railroad commissioners in September, 1883 (and filed in the Maine State Archives in Aigusta) shows a wye in the Monson yard. Two legs are the beginning of the respective Hebron Pond Quarry and Monson Pond Quarry Branches. The third leg was to run from Chapin Avenue to the eastern extremity of the Monson station grounds. I have not seen evidence that the third leg was actually constructed, although the c. 1890 "bird's-eye view of Monson" drawing does portray the wye. Monson's recent proposal to Maine Narrow Gauge raised the possibility of completing that wye.
