Both the 1920 and 1930 census are available at Ancestry.com.HeritageQuest has post the 1920, but not California 1930.If you are not an Ancestry subscriber, check with your local library.You may have access to one or both sites via your library card.You can also try your local LDS Family History Center, who can get the applicable films for you from Salt Lake City.
The Tuolumne Co. Genealogical Society has an outstanding obituary collection, inventories of most of the cemeteries in the county, and access to all of the census records.Be prepared to pay for their research services.[TCGSONLINE.ORG]
You did not say where in the county your ancestor lived.If he was is Groveland-Big Oak Flat-Moccasin contact the Southern Tuolumne Co. Historical Society and include GENEALOGY in your subject line.[GROVELANDMUSEUM.ORG]Check the database online to see if your ancestor is listed.Work is ongoing, so there may be information that is not posted.Again, be prepared to pay for research time. Good luck!