Mo. Rev. Stat. § 256.120: Geodetic surveyors may enter on lands.

Persons employed under an act of Congress of the United States, passed the tenth day of February, 1807, and the supplement thereto, may, upon making satisfactory amends, enter upon lands within this state for any purpose which may be necessary to effect the object of said act, and may erect works, stations, buildings or appendages for that purpose, doing no unnecessary injury.