Here is the site to order California death certificates from. Anyone can order an informational (non official) certificate.http://www.cdph.ca.gov/certlic/birthdeathmar/Pages/default.a...
Sometimes it is quicker to order directly from the county where they died.
Here is the California death index from 1940, where you can find exact death dateshttp://vitals.rootsweb.ancestry.com/ca/death/search.cgi
You can browse the death index for earlier years at www.familysearch.org
By the way, the most expensive (and unnecessary) way is to order it through the vitalchek link on Ancestry.