For openers, you might not be aware that the GM&O itself was a latecomer to the railroad scene, incorporated in the late 1930's as the successor to the Gulf, Mobile and Northern and Mobile and Ohio, The GM&O, in turn, did not venture north of St.Louis until it acquired the Chicago and Alton, usually referred to simply as "the Alton road", in 1946.
For any number of possible reasons, the Alton itself tends to get fairly little attention from the railfan community. Although it served the viable Chicago-Springfield-St. Louis passenger market, it seldom projected an image as a strong competitor to the paralell Illinois Central. During the last years of the 1950's, GM&O operated a Bloomington, Ill,-Kansas City local (former Alton trackage) consisting of only a single self-propelled car that was a 30-year trip into the past. But GM&O was a strange mix of the obsolete and the modern; it is usually considered the first major road to be 100% dieselized (in 1950), and its lack of any "late model" (post-1930) steam power, combined with the generally low levels of both education and incomes along the former GM&N/M&O routes, is probably a major factor in the lack of much historical documentation.
Here are a few links as a starting point:
http://www.gmohs.org
http://en.wikipedia.org/wiki/Gulf,_Mobi ... o_Railroad
http://en.wikipedia.org/wiki/Alton_Railroad
