It doesn't have to be a sandstorm like something from the Sahara that fills up the truck and covers it. That would be extremely unlikely in this area, as the sand is quite coarse and more like decomposed granite chips.
Bundles of tumbleweed mixed in with scrub could easily cover a car, especially if it was upside down in a ravine, where the dirty black underside was showing rather than the bright blue paint.
Of course - I had already addressed ravines. Obviously, tumbleweed could do it, if it were the right ravine. Existing brush could do it, esp if the truck were upside down, as you say.
But elsewhere, not so likely. And certainly less likely if the car were rightside up. I was speaking of a sandstorm absent ALL other misadventure (stuck off road, collision, ravine, etc). When people pull off the road for a sandstorm, they are still near a road. Not likely to be hidden by any sandstorm I've ever heard of in SoCal. And it would have to be tumbleweed season, Imo, for a truck by the side of a road to be covered in them.
I am pretty familiar with SoCal (and AZ and NM) sandstorms. The worst I've experienced were in NM. Still no cars covered up, though. If they were off roading in dunes (was his truck even 4WD? I don't think we've seen any evidence that it was, but maybe), surely he would have carried gear for self-extraction (people get stuck in sand or mud all the time but they don't usually stay in the truck/car until it's covered up by sand or mud). Worst case scenario would be getting stranded with no cell service, which is more the scenario I'm envisioning.
But unless they went off the road into a ravine (or even a small gully or barranca), they should be near a road of some kind. If that's the case, something had to have prevented them from going for help - such as heat. Or, if they did something like spin off a dirt road into rocky territory (unable to self-extract), perhaps they didn't have the resources to walk out. That I can easily imagine - and some of the roads out there are not frequently traveled. STILL, it's a long time for a truck near a road not to be seen.
So, it's either ravine for me or something much more nefarious (or something much more prosaic, such as running out of gas or having engine trouble - there is definitely a reason some desert dwellers want their trucks prepped for sand-wind conditions).
The advice is always to bring plenty of water, just in case; stay with one's car; have some type of bright colored blanket/shade cover. The hurricane hit south of where they were on August 20 - almost a month after last ping from one of them.
IMO
TL;DR being stranded is a possibility - but not a happy one, at all.
