Obtain a Certified Copy of your Marriage License at the County Clerk's Office.

You can purchase a certified copy of your marriage license in person at the County Clerk-Recorder's office in the county you purchased your Marriage License. It usually takes 4-6 weeks after your ceremony before they will have it recorded and be able to send you a certified copy.

You can also order a copy. Contact the County Clerk-Recorders office for your county for specifics at the office, there is usually a downloadable form available for the application. It usually takes 4-6 weeks after your ceremony before they will have it recorded and be able to send you a certified copy.

The San Mateo County Clerk-Recorder's office explains the usual information needed .
"Mailed requests for marriage certificates must include the name of the bride and groom (or Party A and Party B if after June 17, 2008) as they appeared on the marriage license, the date of the marriage and the office where the license was purchased. Marriage certificates can only be purchased in the same county where the license was purchased, regardless of where the wedding ceremony took place. The request should include the address to which the certificate is to be mailed and a daytime contact telephone number. "

Here are the 4 counties in the SF Bay Area

Alameda
http://www.acgov.org/auditor/clerk/marriage1.htm

Santa Clara
http://www.sccgov.org/portal/site/rec/agencychp?path=%2Fv7%2FCounty%20Clerk-Recorder%20%28DEP%29%2FMarriage%20Certificate&contentId=d7a2bb3166b34010VgnVCMP2200049dc4a92____

San Mateo
http://www.smcare.org/clerk/marriage/certified_cm_certificates.asp

San Francisco
http://www.sfgov2.org/index.aspx?page=19

Other Counties

Marin
http://www.co.marin.ca.us

Napa
http://www.acgov.org/auditor/clerk/marriage1.htm

Solano
http://www.co.solano.ca.us/depts/ttcc/county_clerk/marriage_license.asp

Sonoma
http://www.sonoma-county.org/Clerk/HTML_Documents/BDMCerts/Frameset_BDMCerts.htm