Name: Suzanne/Sue Sebastopol, CA (Zone 9a) Sunset Zone 15
Hibiscus was my first thought too, did a Google Lens search to come up with an idea which one and Hibiscus tiliaceus (a synonym now) seems the best match, here's our database entry, yes, huge is an understatement! Sea Hibiscus (Talipariti tiliaceum)
The leaves looks like smaller, fuzzy, and more round. I think that is a Hamabo (Talipariti hamabo). Use to be Hibiscus hamabo, It is in the same genus with Sea Hibiscus, more cold tolerant than other Hibiscus including Sea Hibiscus