A PCN is created by pecking a circular or oval groove in a rock (typically schist in the Bay Area) leaving a raised “nucleated” center that may itself be subject to further manipulation.
For an in-depth study of PCNs see Donna Gillette’s 2011 dissertation Cultural Markers on the Landscape: the PCN Pecked Curvilinear Nucleated Tradition in the Northern Coastal Ranges of California.
Jim examines the protected PCN rock on Ring Mountain. With views like these it’s easy to imagine this rock having special meaning to the peckers of its PCNs.
Check out this video by Alexander Kerekes of the PCN rock on Ring Mountain.