Guess were these engines are.

CLOSE. the black widow used to by the bridge but they moved it. And your way off with the speeder guess. TRY AGAIN.
 
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.

JD