S.D. Codified Laws § 49-34-6
Any corporation organized under chapter 49-33 may extend its railroad, electric light or power line from any point named in its charter or articles of incorporation and may build branch lines either from any point on its line or from any point on the line of any other company connecting or to be connected with its line. Before such extension is made, such corporation shall, by resolution of its directors, to be entered in the record of its proceedings, designate the route of such proposed branch and extension and file a copy of such record, certified by its president and secretary, with the secretary of state and cause the same to be recorded. Thereupon such corporation shall have all the rights and privileges to make such extension and receive aid therefor which it would have had if such branch or extension had been authorized in its original certificate.
SDCL 49-34-6