The photo looks to me to be in the area of Kuhuku Point, the jut of land forming the north side of the Oahu island. The Kahuku sugar fields and mill were nearby and the end of the line for the OR&L. I lived there 3 years while in the Navy. I remember when you rounded Kahuku point, there was a steep flat topped hill that looked just like a mesa in New Mexico. Exactly the geology you see in the background. Kuhuku Point and the north shore was the most exposed during the 1946 and the 1964 tsunami's from Alaskan quakes. The photo would be looking more or less east with the ocean on your left (north). Great photo. You can clearly see how the tsunami surge blew the tracks inland. Not much military along the north shore, so perhaps the military trucks were being used for the tsunami relief aid. When I lived there, there was a narrow gauge engine on static display at the old Kahuku Sugar Mill. Don't know about now.