The trackage was originally built between 1881 and 1882, by the Denver and Rio Grande Railroad, in order to carry silver and gold ore mined in the San Juan Mountains. But it serviced many other mines mining various metals.The line from Durango to Silverton has run continuously since 1881, although it is now a tourist and heritage line hauling passengers, and is one of the few places in the United States which has seen continuous use of steam locomotives.
The GR is for Durango.