Perhaps it was this one, Roaring Camp and Big Trees Railroad, California? There is a second one in working order there.
There are also bigger Shays on a preserved line in the east.
We had some in Australia, on at least three gauges. One is preserved, but not in working order.
Puffing Billy Railway also has one from Taiwan, but as a static museum exhibit.
The Shay was one of several designs for logging railways, with geared drives. They could haul heavy loads on steep grades, but very slowly. They also had the flexibility to cope with sharp curves and rough track.
Roderick B Smith
Rail News Victoria Editor