The communities of Macdiarmid/Biinjitiwabik Zaaging Anishnabek First Nation (formerly Rocky Bay First Nation) are located beside Pijitawabik Bay of Lake Nipigon at Milepost 36.6. Not an original station on the line, Macdiarmid was apparently named after the man in charge of railway construction in the area, William Clyde Macdiarmid; it also may have been named after Findlay George Macdiarmid, the Ontario Minister of Public Works and Highways during the time. It rose to prominence during World War I when it became the centre of commercial fishing on Lake Nipigon and replaced nearby Fairloch (MP 33) as the major railway stop in the area.
The Tunnel, also known as Jumbo’s Cove Tunnel, is located just to the south at Milepost 37.1. It is the largest tunnel in the Thunder Bay area, at 1000 feet long. The two portals and portions of the southern end are encased with concrete and the unfinished appearance suggests more work was intended to be done.
There are photos of the tunnel under construction in the following great article: The Driving of the Last Spike on the Canadian Northern Ontario Railway by John Todd (Canadian Rail Magazine, November 1979)