Hank,
I'm sure they are referring to the fact that in the early 60's, everything was still in place, and that soon afterward things quickly deteriorated and abandonment cut the main to Alamosa.
Also, you have to consider that in the 60's the "Silverton" was actually upgraded and promoted, which made the Narrow Gauge truely profitable for probably the first time ever. Certainly in D&RGW times.
At a minimum, the period of the 50 and early 60's could indeed be argued to be the "peak of operations" of at least more recent history, and by almost any definition of the D&RGW, which succeeded the old D&RG.
I know it seems strange, but I think I agree with it.