At one point years ago(1920's maybe), there was SG from Durango to Farmington, and it was later made NG. Others will know when they converted or check the archives.
As for Carbon Junction, normally trains from Chama were left at Carbon junction and power was taken into the Durango Roundhouse with the caboose.
Then when they would take the load to Farmington the engine and caboose would reverse that.
Yes if the D&RGW survived beyond 1968 they would have kept Farmington, cause that was the reason they kept the line going an extra 10-15 years, the oil and Gas exploration near Farmington.
The fact they made it to 1968 is a miracle really, considering all other class one railroads were dieselized by 1960.
Greg
484 EB at Gato with water train summer of 1966. Photo Greg Scholl
Someone posted a photo of this location without a train. Here is 478 northbound from Farmington on June 3, 1968 with the first train to and from Farmington for the year.
Below 478 heads into Durango from Carbon Junction after dropping the train. The next day the train would go to Chama with 498.