If an estate is in probate, there will be a probate proceeding on file in the Superior Court of the county where the deceased person lived. Check the county probate court records under the Decedent's name. You can access this information on line in several of the California counties. In others, you'll need to either go to the probate court and ask to see the file or mail a letter to the probate court clerk asking if there's a probate in process.
The information you obtain at this site is not, nor is it intended to be, legal advice. You should consult an attorney for individual advice regarding your own situation.