Cal. Civ. Code § 13-40-107.5

(1) The
general assembly finds and declares that:

(a) 
Violent and antisocial criminal acts are increasingly committed by persons who
base their operations in rented homes, apartments, and commercial properties;

(b) 
Such persons often lease such property from owners who are unaware of the
dangerous nature of such persons until after the persons have taken possession
of the property;

(c) 
Under traditional landlord and tenant law, such persons may have established
the technical, legal right to occupy the premises for a fixed term which
continues long after they have demonstrated themselves unfit to coexist with
their neighbors and co-tenants; furthermore, such persons often resist eviction
as long as possible;

(d) In
certain cases it is necessary to curtail the technical, legal right of
occupancy of such persons in order to protect the equal or greater rights of
neighbors and co-tenants, the interests of property owners, the values of trust
and community within neighborhoods, and the health, safety, and welfare of all
the people of this state;

(e) A
tenant who experiences unlawful sexual behavior, stalking, domestic violence,
or domestic abuse is not responsible for the acts of the responsible party,
especially when the responsible party exercises control over the tenant, and
the tenant must not be unfairly penalized or suffer the undue loss of housing
due to the acts of the responsible party.

(2) It
is declared to be an implied term of every lease of real property in this state
that the tenant shall not commit a substantial violation while in possession of
the premises.

(3) As
used in this section, "substantial violation" means any act or series
of acts by the tenant or any guest or invitee of the tenant that, when
considered together:

(a) 
Occurs on or near the premises and endangers the person or willfully and
substantially endangers the property of the landlord, any co-tenant, or any
person living on or near the premises; or

(b) 
Occurs on or near the premises and constitutes a violent or drug-related felony
prohibited under article 3, 4, 6, 7, 9, 10, 12, or 18 of title 18, C.R.S.; or

(c) 
Occurs on the tenant's leased premises or the common areas, hallway, grounds,
parking lot, or other area located in the same building or complex in which the
tenant's leased premises are located and constitutes a criminal act in
violation of federal or state law or local ordinance that:

(I) 
Carries a potential sentence of incarceration of one hundred eighty days or
more; and

(II) 
Has been declared to be a public nuisance under state law or local ordinance
based on a state statute.

(4) (a) 
A tenancy may be terminated at any time on the basis of a substantial
violation. The termination is effective three days after service of written
notice to terminate tenancy.

(b) The
notice to terminate tenancy must describe the property, the particular date
when the tenancy will terminate, and the grounds for termination. The notice
must be signed by the landlord or by the landlord's agent or attorney.

(5) (a) 
In any action for possession under this section, the landlord has the burden of
proving the occurrence of a substantial violation by a preponderance of the
evidence.

(b) In
any action for possession under this section, it shall be a defense that:

(I) 
(Deleted by amendment, L. 2005, p. 402, § 2, effective July 1, 2005.)

(II) 
The tenant did not know of, and could not reasonably have known of or
prevented, the commission of a substantial violation by a guest or invitee but
immediately notified a law enforcement officer of his or her knowledge of the
substantial violation.

(c) (I) 
A landlord does not have a basis for possession pursuant to this section if the
tenant or lessee is the victim-survivor of unlawful sexual behavior, stalking,
domestic violence, or domestic abuse, which unlawful sexual behavior, stalking,
domestic violence, or domestic abuse was the cause of, contributed to, or
resulted in the alleged substantial violation and the unlawful sexual behavior,
stalking, domestic violence, or domestic abuse has been documented pursuant to
section 13-40-104 (4).

(II) 
This subsection (5)(c) does not prevent a landlord from seeking possession
against a tenant or lessee of the premises who is responsible for the unlawful
sexual behavior, stalking, domestic violence, or domestic abuse that was the
cause of, contributed to, or resulted in the alleged substantial violation.