According to "Rio Grande to the Pacific", the first SG track was laid in 1881 near Denver. The D&RG was started as NG in 1870.
The last D&RGW narrow gauge freight line ended operation in 1968 and the last D&RGW narrow gauge was sold off in 1981 (100 years after the first SG rail was laid.
The first D&RGW SG cars (especially when the D&RGW/RGW in Utah was regauged) was narrow gauge equipment on standard gauge trucks (except for the loco drivers of course).
Theis is small snowflake on the tip of the large iceburg of standard gauginging the D&RG(W).
Doug vV