This is the Robert Dollar Shay engine that moved empty freight (box, gondola, and flat) cars from the "hole" across to the mills and then moved the loaded cars back to the hole where the Southern Pacific crews would attach them to trains (called consists) and forward them to their final destination.  The hole was located on the Glendale side of the railroad trestle that went across Cow Creek.  This photo was taken on Feb 3, 1949 by R. Berman.