This line was built in 1902 by the Denver & Rio Grande Western in hopes of connecting to the AT&SF mainline at Gallup, NM (and also to deter AT&SF from building north into D&RGW's territory). At first, the line hauled agricultural products, then in the 1950s, as oil was discovered around Farmington, the line started seeing oil drilling equipment and piping traveling along its route.
This line has the possible unique status of being converted from standard gauge to narrow gauge. (Other lines, if converted, start out as narrow gauge lines and are converted to standard gauge lines.) The D&RGW, with intent on establishing a transfer point with the AT&SF at Gallup, built the line as a standard gauge line, with a change-over to narrow gauge at Antonio, CO, the line's northern terminus. However, the line never made it to Gallup, and the connection with the AT&SF was never made; this line was now considered a standard gauge "island" in an otherwise narrow gauge empire. This, of course, does not make operational sense, so the line was converted to narrow gauge in 1923.
The line was abandoned in the 1960s, and the rails and ties were taken up soon after. Portions of the grade can still be seen along US550; also traces can be found through Flora Vista, Aztec, and Cedar Hill and some of the Animas River bridge crossings are still intact.
At Durango, the right-of-way continues northward to Silverton, and forms the famed Durango and Silverton Narrow Gauge Railroad, an excursion passenger train that runs daily between its namesake towns.
Thanks to Dr. James H. Olsen, Jr., PE for contributing information about this route.