There’s some good sleuthing being done by several readers who have left excellent comments.
It encouraged me to browse around a bit. I tried to search Google for images of OR&L trains, and was surprised to recognize my father in one of the photos. Lo and behold, it seems my sister, Bonnie, has scanned two photos from a later train ride, which she has posted on Flickr. Surprise, surprise!
The photos are captioned December 8, 1946. My dad’s birthday was December 7, so this was probably a birthday party of sorts. I don’t know whether the date was recorded on the original photo by my mother (which is my best guess) or later by Bonnie. I’ll see what she has to say later today.
These later photos certainly confirm that it was a train in the background of the earlier, 1939 picture. No longer any doubt. We still don’t know the location of the 1939 picnic, but this makes the guess of “somewhere along the leeward coast” look pretty good.
So, on to today’s photos.
The top photo shows the train stopped along a sheer, rocky slope. Those windows do look familiar, and are certainly what appears in the older, 1939 picnic photo. It looks like somewhere along the leeward coast, perhaps near Kaena Point?
My dad is with the sitting group. He’s on the right in a horizontal striped shirt. Bonnie is next to him. In December 1946, should would have been four months short of her 4th birthday. Also identified is Genie Pitchford, who had been at the University of Hawaii at the same time as my mother in the mid-1930s.
The lower photo provides a close-up view of the happy group and a different angle on the railroad car.