Cal. Civ. Code § 38-12-803

(1) A
tenant that rents residential real property has the right to be informed of
whether the property has been tested for elevated levels of radon.

(2) (a) 
Before signing a lease agreement for residential real property, the landlord
shall disclose and provide in writing to the tenant the following information
in a document that the tenant signs to acknowledge receipt of the disclosure:

(I) A
warning statement in bold-faced type that is clearly legible in substantially
the same form as is specified as follows:

​

The Colorado Department of
Public Health and Environment strongly recommends that ALL tenants have an
indoor radon test performed before leasing residential real property and
recommends having the radon levels mitigated if elevated radon concentrations are
found. Elevated radon concentrations can be reduced by a radon mitigation
professional.

Residential real property
may present exposure to dangerous levels of indoor radon gas that may place the
occupants at risk of developing radon-induced lung cancer. Radon, a Class A
human carcinogen, is the leading cause of lung cancer in nonsmokers and the
second leading cause of lung cancer overall. A landlord is required to provide
the tenant with any known information on radon test results of the residential
real property.

​

(II) 
Any knowledge the landlord has of the residential real property's radon
concentrations, including the following information:

(A) 
Whether a radon test or tests have been conducted on the residential real
property;

(B) The
most current records and reports pertaining to radon concentrations within the
residential real property;

(C) A
description of any radon concentrations detected or mitigation or remediation
performed; and

(D) 
Information regarding any radon mitigation system, including a system
description and documentation, if a radon mitigation system has been installed
in the residential real property; and

(III) A
copy of the most recent brochure published by the department of public health
and environment in accordance with section 25-11-114 (2)(a) that provides
advice about radon in real estate transactions.

(b) The
tenant shall acknowledge receipt of the information described in subsection
(2)(a) of this section by signing the disclosure.

(3) (a) 
Subject to subsection (3)(b) of this section, a tenant may void a lease
agreement and vacate the premises in accordance with section 38-12-507 if the
landlord fails to:

(I) 
Provide the written disclosures described in subsection (2) of this section; or

(II) 
Make a reasonable effort to mitigate radon within one hundred eighty days after
being notified that a radon measurement professional has determined the air
concentration of radon is four picocuries per liter or more.

(b) On
or after January 1, 2026, this subsection (3) does not apply to a lease
agreement that is one year or less in duration.

(4) As
used in this section, "residential real property" includes:

(a) A
single-family home, manufactured home, mobile home, condominium, apartment,
townhome, or duplex; or

(b) A
home sold by the owner, a financial institution, or the United States
department of housing and urban development.