Covering outcrops along the coast of eastern Santa Cruz Island are these weathered crust that often appear as faces (see Tiger above). The crust appears to be limited to volcanic outcrops. The composition of the crust is suspected to consist of a mixture of guano, slopewash and travertine. The holes in the crust are tanfoni. Tafoni are weathering features that typically develop in groups on near vertical rockfaces. They come in various forms, from honeycomb to caves. Tafoni are prevalent in granular rocks such as sandstones or volcanic breccia. The tiger above is overlying a brecciated volcanic unit in Potato Harbor.
However, due to the excitement of paddling around in kayaks we forgot to take a sample (bad geologists) and so another trip to the Channel Islands is required to conclusively determine the source and composition of these deposits. More research is needed.