This GM&O system map appeared in timetables issued in the 1950s. It was ascribed to Poole Brothers of Chicago, dated 1952. Later versions of this map bear a Rand McNally imprint. I worked for Rand McNally for more than twenty years, taking early retirement in 2001, and knew some of the people who worked on the various railroad maps they published. By the time I was employed there, of course, the GM&O had been absorbed into the Illinois Central Gulf.