Iron Concretion Spheres at Rochester Creek

Last May I visited the Rochester Creek Pictograph Panel just east of Emery, on the edge of the San Rafael Swell. The panel is impressive and I'll try to write up something about it at a later date. While we were there we noticed some odd stains on the rocks near the panel. At first I thought they were bird droppings, but it turns out they were iron concretions in the sandstone.

We mistook these stains for bird droppings

The Fremont sandstone here is very pale and not nearly as red as some other places in Utah. This is due in part to the iron (in the form of hematite) leaching out of the sandstone over the eons as water percolates through it. The iron eventually accretes into small marbles of iron. These are often called "Moki Marbles" or "Moqui Balls." They are frequently found in the lower layers of the Navajo sandstone. In some places on the Colorado Plateau the marbles are almost pure, solid iron. Here they look to be mostly iron oxide and they have formed into shells, with interiors of sandstone. As they weather away they are exposed on the surface of the rock as rings and the weathering stains the rock around them.

A pdf file from the State of Utah, Rainbow of Rocks, explains all this.

A closeup of the exposed and weathered concretions

A closeup of an exposed sphere

A dense concentration along the path to the rock art panel

Here is the location of the rock art panel and these concretions in Google Maps:

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