Cal. Public Resources Code § 7523

No claim shall be made by the State to any land as swamp or overflowed, which has not been returned as such by the United States, nor to lands for which preemption or homestead patents have been issued by the United States, or upon which there are settlers, occupying the land in good faith, who have filed their preemption or homestead declaratory statements. The commission shall not receive any application to purchase as swamp or overflowed lands, any land not returned as such by the United States, unless the application be accompanied by a certificate from the Register of the United States Land Office for the district in which the land is situated, or by the affidavits of two disinterested persons, that there is no preemption or homestead settler upon the land sought to be purchased, or if there is such settler, that he has resided on the land more than six months prior to the time of making such application. The application shall be invalid in every case where there is a valid preemption filing or homestead entry on the land sought to be purchased at the time the application is made.