[greglepore]

What your talking about is referred to in most states as "adverse possession" but Cali uses the prescriptive easement term (which actually means something else in most states, but that's a digression).
I'm not a California atty, but in most jurisdictions once an easement is established it would be transferable with the "benefited" property unless there was some written document saying otherwise.
The "hostile" portion of the test is almost always the crucial inquiry, and I'd seek out some indication that someone in the chain of title can indicate that they gave permission to use A's driveway if you intend to terminate the easement.