The Rio Grande was the epitome of mountain railroading, with a motto of Through the Rockies, not around them and later Main line through the Rockies, both referring to the
Rocky Mountains. The D&RGW operated the highest mainline rail line in the United States, over the 10,240 feet (3,120 m) Tennessee Pass in Colorado, and the famed routes through the Moffat Tunnel and the Royal Gorge. At its height, around 1890, the D&RG had the largest operating narrow gauge railroad network in North America. Known for its independence, the D&RGW operated the last private intercity passenger train in the United States, the Rio Grande Zephyr.
At the end of 1970 it operated 1903 miles of road on 3227 miles of track; that year it carried 7733 ton-miles of revenue freight and 21 million passenger-miles.