The term ST. LOUIS' ___ ARCH refers to the GATEWAY Arch, a 630-foot tall monument located in St. Louis, Missouri. The arch was designed by Finnish-American architect Eero Saarinen and completed in 1965. It is the centerpiece of the Jefferson National Expansion Memorial, which commemorates the westward expansion of the United States. The arch is made of stainless steel and is the tallest arch in the world. The answer to the crossword puzzle is GATEWAY.