Amendments to this charter may be proposed by the City Council by resolution duly adopted at any regular meeting of the Council, and when so adopted, the same shall be submitted to a vote of the legal voters of the City upon the date of any general election in the State of Oregon which may be held after giving notice as provided in this charter. This charter may also be amended by proposal therefor under the initiative provisions as established by City ordinance, or if none exists, then by such provisions, including petition-signing qualifying number and procedures as are provided by Oregon law.