California Code, Public Resources Code - PRC § 3985

All grubstake contracts and prospecting agreements entered into after September 19, 1939, and which may in any way affect the title of mining locations, or other locations under the mining laws of this state, shall be void and of no effect unless the instrument has first been recorded in the office of the county recorder of the county in which the instrument is made.  The instrument shall be duly acknowledged before a notary public or other person competent to take acknowledgments.  Grubstake contracts and prospecting agreements, duly acknowledged and recorded as provided for in this section, shall be prima facie evidence in all courts in this state in all cases where the title to mining locations and other locations under the mining laws of this state are in dispute.