This spur originally ran off the old Big Four/New York Central line that ran along the east side of Powder Mill Road before curving around the north end of the Olin property towards Bethalto. It then continued on through Moro, Dorsey, Bunker Hill, Gillespie, and Litchfield before rejoining the main Big Four/NYC line at Hillsboro. You can still see the old roadbed in Cottage Hills and in Bethalto, where it was used for the Erwin Plegge Boulevard. According to people who lived in the area, I believe the line from Powder Mill road to Bunker Hill was abandoned sometime in the 1950's. The section of the line from Bunker Hill to Hillsboro may have remained open longer, as I still saw some remnants in the 1970'.
KCS now uses the old ICG line.