(Big Arch Rd.) under RR tracks NE of Alton, Godfrey Township, Madison County, IL. Alby St. N. 0.3 miles from jct with MO3/111 (Homer M. Adams Pkwy) in Alton, E. on Big Arch Rd. 0.7 miles (to end) to the tunnel. On private property, ask permission. (N38 55.78 W90 09.90) Photo by Jack Schmidt 2-23-06.