On a bridge abutment crossing old Illinois & Michigan Canal, East side of N. Main Street, Seneca, Illinois.
Spray painted pink. La Salle County.

NGS STATION DESCRIPTION
DESCRIBED BY COAST AND GEODETIC SURVEY 1947

AT SENECA, SET IN THE TOP OF THE SOUTHEAST CONCRETE WING WALL
OF THE STATE HIGHWAY 170 BRIDGE OVER THE ILLINOIS AND MICHIGAN
CANAL, ABOUT 85 YARDS SOUTH OF THE POST OFFICE, 32 FEET EAST
OF AND ABOUT 1/2 FOOT ABOVE THE CENTER LINE OF THE HIGHWAY.