A void marriage is one that isn’t recognized by the court for some reason. In California, these reasons include:
Closely related spouses:
If two spouses are closely related, the marriage will not be valid. California law strictly prohibits marriage between parents and children, ancestors and descendants of any degree, whole or half siblings, and uncles and aunts and their nieces and nephews. These relationships are considered incestuous and no marriage between them will be valid.
Bigamy is also illegal in California. If you already have an existing, legal marriage that has not been dissolved, any subsequent marriage will be void.
Green card marriages:
A fake or sham marriage to obtain U.S. residency is not valid.