Sandstone spheres all over the ground. A GPS device is present for scale.
A closeup view of several of the spheres.
When you look closely at just one of the spheres, you see that they are made up of sandstone and a few of them show inclined bedding planes (or layers), of the type that are found in rivers.
Geologists have characterized sandstone deposition in many environments. Beaches produce cross-bedding with an angle of about 5 degrees. Dunes are very different, because the grains are wind-blown and thus have cross-bedding of about 30 degrees.
Ripples in rivers have cross-bedding that are between these two extremes, which is why I predict that these sands (in the spheres seen above) are from a river deposit. This prediction is consistent with the oxidized red sands and shales that typically form in a desert environment.What is inside of them? I could break some open, but I do not need to. A naturally broken and weathered surface (as seen in the close-up above) frequently shows more detail than a fresh break.
This is a photograph of one of the broken spheres showing rings of an iron mineral called goethite (hydrated iron oxide). We have enough information to make an interpretation.
Recall my previous entry on the spotted sandstone. In that case a bit of rotting organic matter reduced the iron in the rock to form a green spot.
The rock spheres at this site are caused by a bit of organic material that changes the chemistry of the water in the sandstone, causing precipitation of iron minerals. The banding is called Liesegang and you can read all about them by putting in “liesegang rings” into Google.