Hi Bill,

There are no Patellidae native to that region at all, so if you found a
Patella, it would have to be introduced.  There are many species of
Lottiidae there however, and a few of them are sometimes quite
high-arched, especially Tectura fenestrata and Lottia pelta.  Are you
sure you don't have one of these?  They are seldom as heavy and solid as
Patella vulgata though.
Actually I am surprised that limpets have not become more widely
distributed, given their habit of clinging to hard surfaces, like the
bottoms of ships.

Paul M.