Southern Pacific 8321 is the lone helper on an eastbound manifest as it rolls down the hill in Cajon Pass, while an eastbound Santa Fe works up the hill towards Summit.
AT&SF 4-6-4 3456 leads train 2, The Scout, at Wichita Kansas in May of 1940. Note the clanging bell, and rods down, at 25 MPH. Otto Conrad Perry photo, from my collection.