Moqui marbles in Utah. They seem to be the end-result of spherical weathering. Note their distribution along the joints in the sandstone. Looks like a good place to conduct a stoning.
Or getting stoned.
That’s very weird. I never heard of them or saw them in my years in Utah, and I’ve hiked through many of those sandstone areas. The article (and others I checked online) didn’t give the locations of the Moqui beds.
The picture the OP posts shows circular voids in the bed of Moqui Marbles (Not all such pictures do – http://www.livescience.com/47936-how-moqui-marbles-form.html ), which looks similar tro circles caused by “frost sorting”: