Where one spouse has died and there is a conflict over title to property you would do best to consult a California probate attorney in the area where the property is located. The answer could be difficult because the application of "tracing" laws is different on death than in the case of divorce.
If you are claiming an interest in community property, the answer will depend partly if there was a will or trust involved, and the way the property was titled. If as "husband and wife as joint tenants (or as "community property") with right of survivorship" the burden will be on you to establish that the deceased spouse did not intend the surviving spouse to inherit the whole property. Your chances improve if there is no reference to "right of survivorship."
I hope that helps.
This answer is not intended as legal advice, and no client attorney relationship is established.
Under California law, there is the right to reimbursement under Family Code section 2640 (link below) for all separate funds that a spouse contributed to the "acquisition" (as defined in the Code) of a community property residence.
I do not represent the person who asked this question, and was not given enough information to provide a better answer. The limited information is enough to indicate that a consultation with an attorney in your area is necessary and advised.
You may recieve some reimbursement for any separate funds you contributed to community property, you shoudl check with a local CA attny for specific issues. take care and good luck.
Legal disclaimer: The response given is not intended to create, nor does it create an ongoing duty to respond to questions. The response does not form an attorney-client relationship, nor is it intended to be anything other than the educated opinion of the author. It should not be relied upon as legal advice. The response given is based upon the limited facts provided by the person asking the question. To the extent additional or different facts exist, the response might possibly change. Attorney is licensed to practice law only in the State of Massachusetts. Responses are based solely on Massachusetts law unless stated otherwise.