It would probably be useful to read about California probate law and the duties of an executor (PolyGeo's link to Wills, Estates, and Probate page of the California Courts is a good place to start). In most jurisdictions, there is a requirement to show that a reasonable search has been done to find and contact all the heirs. There are also likely to be provisions in the law to deal with the consequences if an heir comes forward after the case is closed.
There are even heir-search companies that track down the heirs of difficult (and lucrative) probate cases for a cut of the inheritance. (I had one such company contact me a couple of years ago, because a distant cousin had died in California, and her siblings in Germany were named in my website).
Most likely, you were never named in the relative's will, but good luck if you wish to pursue the issue.