Barstow was an important spot on Route 66, and that's a good reason for you to have the name in mind when remembering the trip to Orange.
The city does have a very old motel (El rancho) which looks pretty similar to this one you have in this picture. However, I could not find any place in town with such a mountain view. See some Barstow pics here.
The closest mountain view I've found is actually a picture taken from Hacienda Heights (west coast).
I think you should not disregard the possibility that this picture could have been taken after crossing the mountains. If you look at the map with a terrain view, the valley near Riversdale has great chances.
The motel in the picture looks small, probably got sold and repurposed, making difficult to identify it from nowadays photos.
If you wish to share this amazing pic and also get some extra guidance to locate it precisely, you could join the Route 66 historic group on Facebook:
If you get the point, let us know! :)