The line originated as a part of the Canadian Northern Railway (CNoR) mainline, which was pushing eastward from the Prairies in an effort to connect its network to Montréal.

[1] After the Canadian Northern's amalgamation with other railways, resulting in the Canadian National Railway (CN), the line was used as CN's most direct route between Québec and the Prairies, paralleling the competing CP North Bay Subdivision to the north along its eastern stretch and the CP Cartier Subdivision to the south along its western.

[3] Its main use, however, was as a freight railway, with large amounts of timber from the mills at Kiosk, Fossmill, and Skead, as well as ore from Crerar, being transported along the line.

This resulted in the ex-CP Canadian from Toronto to Vancouver as the primary transcontinental passenger service and CN's Super Continental as the secondary one.

[8][9] In 1981, Via Rail experienced its first wave of significant cuts, sometimes called "Pépin's Axe" in an evocation of the 1960s Beeching Axe in the United Kingdom, under federal Transport Minister Jean-Luc Pépin (a member of Pierre Trudeau's Liberal cabinet), resulting in the cancellation of the Super Continental and making restoration of service along the Alderdale Subdivision increasingly unlikely.

[17] A number of existing communities along the line were devastated, such as Kiosk, where residents were forced to leave and their houses were demolished by the Ontario Ministry of Natural Resources as they fell within the boundaries of Algonquin Provincial Park.

[4] By the early 2000s, a local community group, Rainbow Routes, was organized to promote the conversion of the section from Capreol to North Bay to a rail trail.