The original group of cars was designed by some consultant types by the Commission. The railroad, then operated by Scenic Railways, had no input in the design or the construction. when the cars were finished, the Commission told Scenic Rys, "Here ya go, run them. They're all named for places in the San Luis Valley, so you have to use them on the east side..." The first cars came on line in the spring of 1982.
The second batch was batch was designed and built by the RR under Kyle Railways, the operator. The initial design concept was literally scissors-drafted by getting a O Scale drawings of a 6500 class flat and a passenger coach (I think from Central America) and making the passenger car body fit on the frame by cutting the drawing up. The details came later.
Dan Ranger, the GM had come from the LK&P in Hawaii. Several of the design features of the cars - fiberglass siding that looked like wood, larger than normal windows that slid down into the car body below the belt rail - came from cars built for the LK&P.
The second generation cars came along starting in 1987.