Hi Jonathan! Thank-you for contacting us through the Southern Pacific Railroad History Center Forum. Unfortunately, in a search of our files, we have not come across anything connected to a John Milton Campbell. It would be interesting to discover where your great grandfather worked in California on the Southern Pacific. If you are willing to share some of his memoirs surrounding his experiences on the railroad we would be willing to publish some of them for our membership and friend base. As further info, Southern Pacific did not operate in the state of Colorado until the 1990s, so maybe your great grandfather worked for another railroad as well prior to Southern Pacific. You can contact me for questions or comments at pkbaumhefner@comcast.net