Are these igneous Liesegang rings on a popular Oahu, Hawaii hike?
Not knowing the setting and judging from the image alone in this trampled environment, I think we're looking at a form of chemical weathering called &quot;spheroidal weathering&quot;.
The gist is this (from the linked wiki page):
Penetrating water alters the bed-rock along cracks or joints, causing volume changes between altered and unaltered parts. These differences result in the formation of spheroidal layers that are removed by erosion (or trampling), leaving a central relatively unaltered boulder/pebble.
Liesegang rings are somewhat enigmatic, not sure if the term is applicable here.