California Code, Code of Civil Procedure - CCP § 349.4

All acts and proceedings heretofore or hereafter taken under color of law for the formation, organization or incorporation of, or for any change in the territorial boundaries of, any city, county, city and county, special district, public corporation or other public entity, or improvement district, annexed area or zone within any of the foregoing, and for the authorization, issuance, sale, or exchange of bonds of the entity or the territory thereof may be confirmed, validated, and declared legally effective in the manner provided in this section.

The legislative body of the entity may instruct its clerk or secretary to mail a notice to all owners of property within the entity, within the improvement district or zone, or within the annexed area, as the case may be, as their names and addresses appear on the last equalized county assessment roll, or as known to the clerk or secretary. Such notice shall include the name of the entity, the date the entity or the zone or improvement district therein was ordered formed or its territory changed by annexation or otherwise, as the case may be, the amount of bonds authorized, if any, and a statement that commencing with the date of mailing of said notice there shall be a 60-calendar-day period during which period any property owner may file an action contesting the validity of the formation of the entity, or of such improvement district or zone, or of such change of boundaries by annexation or otherwise, as the case may be, or the validity of the bond authorization, if any. The clerk or secretary shall make and file with the legislative body of the entity a certificate of mailing of the notices. The legislative body of the entity may order the clerk or secretary to include in such notice such other additional information that it deems pertinent.

If no action is filed during such 60-day period, the formation of the entity or of such improvement district or zone, or the change of boundaries by annexation or otherwise, as the case may be, and the bond authorization, if any, are valid and uncontestable.