Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The City of Denver was a passenger train operated jointly by the Chicago and North Western and Union Pacific railroads. The train operated on both railroads' rights of way between Chicago, Illinois, and Denver, Colorado. In 1955 the Milwaukee Road assumed the service, replacing the Chicago and Northwestern between Chicago and Omaha. This train service was the fastest long-distance passenger train in the world when it debuted in 1936, traversing the 1,048 miles in as little as 16 hours.