Found these at the Canadian archives. Except for Billmeyer & Small and Jackson & Sharp builders photos of early D&RG rolling stock, the Merrilees Collection doesn't have a lot from the Colorado narrow gauges. There is a fair bit on other very early USA narrow gauge lines however, and here's a couple, along with a portrait of the Jackson & Sharp works.
From what I can gather in Hilton's "American Narrow Gauge Railroads", the Cherokee RR in Alabama was possibly the first USA common carrier narrow gauge, the 3' gauge portion of the line built in Nov/Dec 1871. Hilton has a photo of their locomotive, but perhaps this equipment shot is new.
The Central Valley RR was in New York state, and was among the most short-lived narrow gauges. He says the line was opened in May 1872, but was dismantled in April 1875.
This picture appears in the same archives folio - a shot of the J&S works. All the photos appear to have age, and are certainly not modern copies. My apologies if these shots are old news, but they fascinated me and may be of interest to some of you.
Cheers,