Easter-Island-like Heads in the Sand

[alakshak]

I have made a list of many favorite stories and so can sometimes provide title and author answers to a story plot, but one has been eluding me. A small in-atmosphere scout ship with a small human crew see below some giant stone heads with green eyes, which disappear and reappear, making them hard to substantiate and study. When they land among the heads, the narrative says the heads moved and... gulped. They were not statues, but were themselves life forms living in the sand. There were no people left to make the report back. All was sand, as it had been before.

It was horrifying even with the funny incrongruity of seeming statues gulping.

Any help would be appreciated so that I may re-read this intriguing tale.