Hi Liz, I didn't find anything for Alice Back using b. 1891, CA and looking for marriage info. However, I think she's a GOOD candidate for being your Alice Back. If she was in an orphanage for many years, she probably wasn't given her accurate birth place and where her parents were born.
I'd look in San Francisco Co. for her marriage license at www.sfassessor.org/index.aspx?page=16 . Their web site isn't the most clear but does provide contact info. Successful Searching!