Hey Bobbi;-
      I was born and raised in SF also. There's a nice beach west of
Muir Woods as I remember that may have some decent shells. In most
cases along the Pacific Coast, the incoming surf is so high and heavy
that most beach shells are reduced to sand grain size before they hit
the beach. South of Santa Barbara, it's a lot better. I went to Grant
School and Lowell High, and lived by Lafayett Park on Sacramento
Street.
Where do you live now?
          Art