Legal Question in Real Estate Law in California

Perhaps. It depends on what his will or trust says, if he has one. If not the laws of intestacy apply to direct who is the recipient. A lot more information is required to answer your question. You (and he) should engage an estate planning attorney.

There should be a deed or a trust that answers your question. I have clients that were left everything but the gas and oil rights.

Mineral rights, unlike ownership of the land itself, can be abandoned. See the California Supreme Court case of Gerhardt v. Stephens. Therefore, you have two separate questions to answer: (1) whether the rights remained in effect at the time of his death, and (2) who is the rightful heir. Spouses usually inherit from one another, but that depends upon whether the property was held as community or separate property, and in the latter case, what the deceased spouse's will or trust says about that particular property.