The title was probably referring to the amount of traffic on the Cumbres line during the Farmington gas boom, although the peak there would have been in the 50's not 60's.
There are probably a lot of ways to measure peaks, with different times.Narrow gauge mileage, train starts, train mileable, tons, and ton-miles.It would not surprise me if in terms of ton-miles that the peak was indeed during the Farmington gas boom, ie, mid-19650's. And that traffic was still substantial into the early 1960's. I would guess that ng. track miles might have peaked around 1890, train starts or train miles maybe in the 1920's, and tonnage during the 1950's
I'm away from my library, but it would be interesting if any one can add any facts.
JBWX