Cal. Civ. Code § 9-107.5

Notice to unknown occupants.
(a) Service of process upon an
unknown
occupant may be had by delivering a copy of the summons and complaint naming
"unknown occupants" to the tenant or any unknown occupant or person of the age
of 13
or upwards occupying the premises.
(b) If unknown occupants are not named in the initial
summons
and complaint and an eviction order in favor of the plaintiff is
entered, but the
order does not include unknown occupants and the sheriff determines
when
executing the eviction order that persons not included in the
order are
in possession of the premises, then the sheriff shall leave with a person of
the age of 13
years or upwards occupying the premises, a copy of the order, or
if no one is present in the premises to accept the order or refuses
to accept
the order, then by posting a copy of the order on the
premises. In
addition to leaving a copy of the order or posting of the
order, the
sheriff shall also
leave or post a notice addressed to "unknown occupants" that states unless any
unknown
occupants file a written petition with the clerk that sets forth the unknown
occupant's
legal claim for possession within 7 days of the date the notice is posted or
left with any
unknown occupant, the unknown occupants shall be evicted from the premises. If
any
unknown occupants file such a petition, a hearing on the merits of the unknown
occupant's
petition shall be held by the court within 7 days of the filing of the petition
with the clerk.
The unknown occupants shall have the burden of proof in establishing a legal
right to
continued possession.
(c) The plaintiff may obtain an eviction order only and not for rent
as
to any
unknown occupants.
(d) Nothing in this Section may be construed so as to vest any rights to
persons
who are criminal trespassers, nor may this Section be construed in any way
that interferes
with the ability of law enforcement officials removing persons or property from
the
premises when there is a criminal trespass.