It is actually the Pacific Locomotive Association/Niles Canyon Railroad. SP5623 is (last I heard) still owned by Howard Wise and Errol Erman but given a home with the PLA.
This is also a historical portion of the continuation the the Central Pacific on its eastward expansion and both SP and WP had tracks through the canyon. Now it is all UP - sad to say.
I would really enjoy more pictures, feel free to email me them directly if you like. Would enjoy more pictures of the skunk and any black widow stuff you might have too. Thanks!