New Travel Plans

I'm going on a little California trip this Friday
and will present some new work at a conference in San Diego. The whole conference will almost take a whole week and after that I'll spend three days in Southern California for fun. I'm thinking about getting a rental car and going somewhere. The question is where. Major attractions like Grand Canyon or Monument Valley are about eight hours away. Mexico is quite close, that would be an option.
Another thing that sounds very interesting to me is "ghost towns". In California are a lot of old and abandoned gold-mining towns in the desert. Some of them are totally left alone, some others are turned into tourist attractions. I personally started to be fascinated by ghost towns after I accidentally found one here in Jersey last winter (an abandoned soul asylum).
Here is another idea: I'm a big Back to the Future fan and seriously thinking about driving to Los Angeles and visiting all the places where this movie takes place. Mostly very unspectacular streets and residential areas, but after seeing this movie a thousand times, I would be very excited being there. Can anybody understand this? :-)
If someone has other ideas, let me know!