1604. A certificate of purchase, or of location, of any lands inthis state, issued or made in pursuance of any law of the United
States or of this state, is prima facie evidence that the holder orassignee of such certificate is the owner of the land described
therein; but this evidence may be overcome by proof that, at the time of the location, or time of filing a preemption claim on which the
certificate may have been issued, the land was in the adversepossession of the adverse party, or those under whom he claims, orthat the adverse party is holding the land for mining purposes. (California Evidence Code Section 1604)