Pretty sure I've got them in the USA Fed census 1900 for San Diego Ward 7, California:
Mertzman, Harry born Dec 1868 Penn, parents born Germany
" , Mamie Aug 1872 NEW YORK, parents born Germany
" , Bernard July 1893, California, parents born Penn, NY
Harry is a butcher. He and Mamie have been married eight years. Bernard is the only child born to Mamie so far.
So, the best would be to find their marriage record from about 1892. Do you think they were married in California? Often, the bride & groom's parents were named on the marriage record. Good luck! -NGP