I was there today too.
The locomotive on Grand sierra scenic RR was built by Crown metal products. It was assembled in 1983 just for Knott's Camp Snoopy area. The boiler was actually built in I think 1979, then stored for later use. The Crown catalog called them "little toot". Its 24" gauge and burn's propane, with an operating pressure of 170 psi (max is 200psi). Ours is also probably the most modified cosmetically.(for the better) The coaches are from Crown as well.
Crown built these loco's as amusement park rides. They made the "little toot" 4-4-0s in 15" and 24". They could burned coal or propane. They also made 3-" and 36" models.
You can find some info if you do a search on the web. There are still some others operating, and some in private hands.
This is what ours looked like as built.