In 1909, the Minneapolis, Saint Paul and Sault Ste. Marie Railroad, the "Soo Line", built a number of spurs west of Lawler Junction (see Gully to Duluth) in order to access a number of iron ore mines in the area. The main spur branched from the Soo Line's mainline at Lawler Junction and went through Aitkin and Rabbit Lake Township, where it split into two branches. The first went south through Deerwood and to mines to the south; the second continued west to other mines. In 1914, the Soo Line extended the Cuyuna District to Iron Hub and Iron Mountain (now Trommald).
Abandonment of the majority of the Cuyuna District came in 1930, leaving only a small spur between Crosby Junction and Crosby, which itself was eventually abandoned in 1987.
A number of towns sprang up along the Cuyuna District during its heyday, including the towns of Cuyuna, Crosby, and Ironton. Some of the smaller communities are now ghost towns.
Thanks to Adam Jelinski for contributing information about this route.