Like many other mines of the same era, coal at the Greenhill mine in Crowsnest Pass was dug out by miners working underground. Good air circulation was essential, both to prevent the build-up of explosive methane gas released by mining activities, and to enforce air exchange so miners could breathe. Temperature differentials between air at the surface level and below ground didn’t permit sufficient air movement without assistance, which was provided in the form of large intake / exhaust fans. Depending on the geometry of the active mine shafts and the surface vs. below-ground temperatures, the fans might be set to exhaust warmer air from below or push down warmer air from above. Typically a major network of shafts would employ one or two primary fans and then potentially several smaller auxiliary fans over outlying ventilation shafts. From the size of this fan unit, it appears to me to be an auxiliary. For decades now, since the mine closed in 1957, this fan’s tree-sheltered blades have had no force to them, perhaps only rocking a bit in reaction to the strong winds that blow through the Crowsnest region.