Actually it's not the economy, it's the cost of new cars/trucks in general. I just can't afford one, and probably never will, so I bought used.
There are a couple of other reasons for that as well.
California doesn't require smog checks on pre-1981 vehicles, so better to keep the ancient POS running as long as possible.
Next, it's more difficult for an illegal to prove residency in order to buy/finance a vehicle, so a lot of the immigrant population goes to local lots and gets a used vehicle. Since older vehicles tend to be easier (read: less computer crap) to maintain, that's also working in their favor.