Good thoughts. Here are a few observations/comments for what they are worth.
I believe that the investigators narrowed the date of death down somewhat to the previous spring (1958). I do not recall how that was accomplished, but there are several possibilities. With all the items found at the site, there would be some ways of telling when they were manufactured.
As mentioned in previous posts, the barrel date of the rifle would provide one clue. The ammunition boxes would also have been marked with a lot number associated with a date. The money found on the body, or with his effects, would also have dates on them, as did the books. With those sorts of clues, one could determine a date that the death could not have occurred earlier than.
Other forensic clues from the body could also have pointed to a general date or time frame. For instance, there was no cold weather clothing, which would tend to rule out a winter camp.
As to the leather jacket, I can say from personal experience that they are truly an "all weather" item. When it is hot, the jacket makes you hotter. When it is cold, the jacket is cold. When it is wet, the jacket gets wet too. While providing a certain amount of protection and warmth for the motorcycle rider, and of course looking very cool, they are not the choice of any serious camper or hunter.
The most likely scenario regarding a vehicle is that he parked it at the freeway oasis and hiked back to his campsite. After his death, the vehicle (whether car or bike) was either towed away by state officials as abandoned. Or it was stolen by someone who noticed that it had been left there.
It is most likely that he did have a vehicle of some sort, because to walk would have meant carrying all that stuff on his back for many miles to have arrived at the site. And even if hitchhiking, who would pick up a man carrying a rifle? And why would they leave him at a remote highway oasis?
