The Denver and Rio Grande Western Railroad (reporting mark DRGW), generally referred to as the Rio Grande, originally the Denver and Rio Grande Railroad, is a former U.S. railroad, having been absorbed into a larger system — Southern Pacific Transportation Company — as the result of a merger. The D&RGW served mainly as a transcontinental bridge line between Denver, Colorado, and Salt Lake City, Utah, and a major origin of coal and mineral traffic, with a motto of Through the Rockies, not around them. The Rio Grande was the epitome of mountain railroading, operating the highest mainline rail line in the United States, the over 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 longhaul passenger train in the United States, the Rio Grande Zephyr.