From MARRIAGE RECORDS OF SAN JOAQUIN COUNTY CALIFORNIA VOL III compiled by San Joaquin Genealogical Society 1975...on page 1: Joseph Acker married Frances Wilkinson April 17, 1888.
This extracted info was taken fom Vol. 5, page 365 of the MARRIAGE RECORDS OF SAN JOAQUIN COUNTY CA.
I think you can find that vol. and page at the Recorder's Office in Stockton. The book where I found the info was published by the San Joaquin Genealogical Society. You can find their web site via Internet.