No railroad exists in a vacuum, and the Rio Grande had some very interesting connecting railroads. Some were interesting but purely independent, and some were an integral part of the Rio Grande story.
The Denver, South Park & Pacific was a direct competitor to the D&RG narrow gauge in early days, racing to build a line over the Continental Divide towards the mining riches of Leadville, CO?, and Gunnison, CO?. In later years, several of its narrow gauge lines were added to the D&RG system while other parts were abandoned. The final segment - the line from Leadville? to the Climax Mine? - was converted to standard gauge in 1943 and continued shipping outbound traffic via the D&RGW Tennessee Pass line `for decades.
Built by Otto Mears around the west side of the San Juans, the RGS was constructed to serve the booming precious metal mining industry. The D&RG acquired a controlling interest in the RGS in 1895, and maintained it until the end in 1951. Much of the older D&RG equipment went to the RGS.
The Uintah Railway connected Mack, CO?, on the Rio Grande's Utah Desert mainline, with the gilsonite mines in the Uintah Basin to the north. It was completely independent of the D&RG/D&RGW/RGW, and was a common carrier company railroad of the Gilson Asphaltum Company.