Re: Sumpter Valley Ry...

The Santa Cruz (CA), Big Trees and Pacific sits in your idled for a time category. About 12-14 miles long, mostly tourist but hauls freight on occaision and may haul more in the future. And it was originally a narrow gauge line: South Pacific Coast.
The Pacific Locomotive Association has relaid about 10 miles of track on the former Southern Pacific (originally first Western Pacific) line in Niles Canyon, CA.
Both of these, however, do not run completely accurate, vintage equipment.
The Grand Canyon Railway (~64 miles) does not run vintage equipment, but it is probably one of the few "tourist" railroads still performing its original FUNCTION, which was to haul passengers to the Grand Canyon.
And then there is the California Western Railway, perhaps the grandaddy of all "preserved" railways on the west coast. It is still operated under the same name, still a common carrier, still using equipment that, for the most part, it purchased for its "legitimate" operations. It has never completely abandoned passenger service, and still hauls freight (when the NWP is giving connections). And it is reviving one of its own steam locomotives for service.
However, I have to admit, its is REALLY hard to beat the EBT, D&S, C&TS and WP&Y for history and historic veracity.