I saw it on TV sometime in the 1980’s. All I remember is one scene. A guy is out in the middle of the desert in an RV. He looks off the in the distance and sees a rock rolling across the desert floor. There’s nothing pushing it … it’s just tumbling along like a tumbleweed. It was a very creepy image.
Any ideas?
Rock? Horror?
Rocky Horror Picture Show?
The only thing that I can think of that vaguely fits is Damnation Alley
It sounds vaguely like something that could have happened in one of the Critters movies - the first ones too place in a desert town, and the Crites tended to roll around. Single rolling Crites, due to their fur, would look more like tumbleweeds than rocks, granted, but the Big Ball O’Death mass of them would look rather like a lumpy rock from a distance.
Sounds like Tremors, specifically the scene where the giant worms grab the doctor who lives in the middle of the desert in his RV.
But they don’t move a giant rock, it’s a generator. And Tremors didn’t start getting shown on TV until 1990. But it’s the closest movie I can come up with.
EDIT: Tremors like on IMDB: Tremors (1990) - IMDb
Nope, not Tremors, **Critters ** or Damnation Alley. I’ve seen all of those and they’re definitely not it.
I asked my horror-movie aficionado husband, and the only one he can think of involves Mars - but just in case you misremembered the RV part, I’ll explain the rest. He doesn’t recall the title of it, but it’s an exploration of Mars where no life is found even though there might appear to be signs of it. All of the life is silica-based, and “comes alive” when exposed to iron-rich fluids… like blood. He thinks there might have been a similar scene, obviously without an RV in it.
Ghosts of Mars? Mission to Mars?
He says it’s neither of those; he knows those two films. But thanks. 
I don’t think it was set on Mars. I pretty clearly remember that it was the American southwest. The guy’s out in the desert and sees something off in the distance. He looks closer (maybe through binoculars?) and sees that it’s a rock (or a boulder) rolling toward him through the desert, just tumbling end over end for no apparent reason. It’s spooky and creepy and he’s freaked out by it.
But now you’ve got me doubting my memory. Maybe I blocked out all the science fiction elements. If your husband remembers any more about it, let me know.
I remember the production values being pretty crappy, like it was a 1970’s grade-Z horror movie. It’s also possible that it was a made-for-TV movie.
I asked at a horror board. Tom Picirrilli always knows these. He says:
"It might be an episode of THE OUTER LIMITS called “Cry of Silence” starring Eddie Albert.
In it, Albert and his wife are stuck in a California desert after their car breaks down. An alien lifeform possesses boulders, rocks, weeds, and tumbleweeds which move on their own, chase after the couple, and attack them after they’re holed up in a shack."
FYI, that episode is on Volume 3 Disc 1 of the DVD set (which apparently is a re-issue?). I just added it to my Netflix cue. Thanks for reminding me of that episode. Even if it isn’t what you’re looking for, that particular DVD has "Behold, Eck!" and “Demon with a Glass Hand”, two of my favorite episodes.
Ooooo … that sounds really promising! And in the mental picture I have of the scene the guy looks kind of like Eddy Albert. I bet that’s it. Thanks very much.
Today I found myself thinking about the scene with the rolling boulder in the desert again. I’d forgotten that I’d started this thread, but I discovered it again through Googling. However, when I went and watched the Outer Limits episode on YouTube I discovered that it WASN’T what I remembered.
However, further Googling led me to a plot summary on the IMDB for an obscure 1977 horror movie called Ghosts That Still Walk. And lo and behold, the trailer on YouTube contains the desert scene that I remember. Which is still creepy as hell.
Victory!