Monocraterion on the bedding surface of a sandstone of the Early Cambrian Campito Formation (probably Montenegro Member), Inyo Mountains, Inyo County, California.
For similar, see Hollingsworth (2005) fig. 7
Hollingsworth, J. S. 2005: The earliest occurrence of trilobites and brachiopods in the Cambrian of Laurentia. Palaeogeography, Palaeoclimatology, Palaeoecology 220:153–165.