Hi Charlie,
I think you mean Patelloida saccharina.  I'm not aware of a Patella by that
name.  Also, there are no Patella species in California.  The Californian
species which most closely resembles Patelloida saccharina is Acmaea scabra
Gould.  However, P. saccharina is exported from the Philippines literally by
the ton for craftwork, and I wouldn't be too surprised to find a couple of
specimens that someone dropped almost anywhere.
Regards,
Paul M.