Cal. Gov. Code § 25376
Notwithstanding anything in this chapter to the contrary, the board of supervisors may convey, upon such terms and conditions as the board determines to be in the public interest, any surplus real property, together with any building thereon, owned by the county which has been determined by the board to be of general historical interest, to a county historical society, which historical society is a nonprofit corporation formed under the laws of this state. Any such conveyance shall contain a condition to the effect that the historical nature of the property be restored, preserved, or both, for the benefit of the citizens of the county, and that title will revert to the county in the event that the historical society conveys the property in question to any person or entity which is not a nonprofit corporation involved with preserving and researching the history of the county.
Ca. Gov. Code § 25376