The exercise of any or all powers granted by this part shall be authorized and the bonds shall be authorized to be issued under this part for the purposes set forth in this part, by resolution or ordinance of the governing body of the city or county which shall take effect immediately upon adoption. Any such resolution or ordinance shall set forth a finding and declaration (1) of the public purpose therefor and (2) that such resolution or ordinance is being adopted pursuant to the powers granted by this part. The finding and declaration shall be conclusive evidence of the existence and sufficiency of the public purpose and powers.