2' 6" gauge on that Patagonia railroad sounds like it may have ben originally built for ore, never passenger service.
I've read the reason for such a narrow gauge is it allows much shorter radius curves, so there's less earthmoving to build a route in rough terrain. And on this Patagonia route, there may have been cheap construction and poor maintenance, expected to last only until a mine's ore was exhausted.
Dad related to me that as a kid, he worked summers for his father at a gold mine in the Sierras. His father was the mine superintendent. Dad chucked worthless rock off the conveyor as it went to fill narrow-gauge railcars. That railroad ran 30 miles to Colfax where the cars were dumped into the transcontinental SP train. The ore went to Oakland, then by barge to the smelter at Tacoma Washington. Barely profitable. But during the Depression, better than closing the mine.