I found this on the bank of the Fraser River in BC, and at first I thought it was a piece of wood. But when I picked it up, I realized it wasn’t. Does anyone know what formed the rings? Is it even a rock?
It is a rock showing color bands of iron oxide. The color banding is most likely the result of moisture penetrating the rock and causing the iron to go into solution and migrate. This process produces the color bands present in the rock.
This commonly seen in sandstone formations containing iron bearing minerals. Here is an article that does a nice job illustrating how water causes iron staining. Although your rock does not appear to be sandstone, the same process applies to igneous or metamorphic rocks.