There are only a couple within an hour or so in either direction. I've never noticed a seemingly permanent population; rest areas in populous areas are patrolle

There are only a couple within an hour or so in either direction. I've never noticed a seemingly permanent population; rest areas in populous areas are patrolled regularly by police, and California has an 8 hour limit on stops. It's actually pretty rare to find folks spending more than a day or two at rest areas even in places where police don't visit often. So, no, I'd bet there is no near-permanent residency happening at rest stops in Northern CA. At least, I've never seen evidence of it. And, I sometimes talk to folks living in weird places when I find them, as I find the subculture fascinating (if a little depressing). I've met lots of Walmart parking lot residents. But, no Walmarts in Northern CA allow overnights, either.