Just found these pictures of the Argentine Central Railway from the Colorado State archives website. It was the railroad that joined up with the Georgetown Loop. It was a tourist railway for the most part that ran up to the top of Mt. McClellan, but never on Sundays. It was owned by a pastor and because he didn't want trains running over his railroad on the "Lord's Day," he took an enormous hit each week in revenue during the tourist season. As a result, the railway folded in a few years but kept opening under other names. There were some mining ventures, but the rails were eventually torn up by the 1920's in the places where nature didn't already remove the presence of a railroad.
Today, a jeep trail leads almost all the way up. To track it further, look up Tracking Ghost Railroads in Colorado by Robert Ormes.