The other box was simply an intermodal storage container, but this one was a portable office for the Union Pacific North/West "Tie Gang" (the crew that replaces railroad ties, an unending task on a railroad) that had come through here a while ago.
When a truck showed up to haul away the other container, we walked over and told the driver how grateful we were that he was taking the trailers away, because they had been blocking our view of the railroad for a couple of weeks. He looked at us a bit oddly and told us that he expected the other trailer would be removed the following day. That morning, we got out and took these photos of the portable office.
There are more pictures, including close-ups and details of the generator mounted on the front of the container, on Flickr.
Shortly after we took this second photo, we went for a walk, and when we returned, the trailer was gone and our view of the railroad restored.