The Telgraph wires

Telegraph wires were hung along railroad lines in America since 1861. So it is entirely possible that River City Iowa would have Telegraph wires in 1912.

Somebody saw fit to assert that the wires visible in the upper screen when Harold Hill walks in the direction of River City were misplaced wires from Warner's Brother's back lot. Telegraph wires were a fact of life along railroad tracks in 1912 America.