California Code, Insurance Code - INS § 10384.17

(a) A health insurer shall not rescind a health insurance policy, or limit any provisions of a health insurance policy, once an insured is covered under the policy unless the insurer can demonstrate that the insured has performed an act or practice constituting fraud or made an intentional misrepresentation of material fact as prohibited by the terms of the policy.

(b) If a health insurer intends to rescind a health insurance policy pursuant to subdivision (a), the insurer shall send a notice to the policyholder or insured via regular certified mail at least 30 days prior to the effective date of the rescission explaining the reasons for the intended rescission and notifying the policyholder or insured of his or her right to appeal that decision to the commissioner pursuant to subdivision (b) of Section 10273.4.

(c) Notwithstanding subdivision (a) of Section 10273.4 or any other provision of law, after 24 months following the issuance of a health insurance policy, a health insurer shall not rescind the policy for any reason, and shall not cancel the policy, limit any of the provisions of the policy, or raise premiums on the policy due to any omissions, misrepresentations, or inaccuracies in the application form, whether willful or not.  Nothing in this subdivision shall be construed to alter existing law that otherwise applies to a health insurer within the first 24 months following the issuance of a health insurance policy.