It followed Riverside west and onto a curvy section near the confluence of the Big Sioux and Missouri rivers .
US 20 turned east onto 5th Street and US 77 turned west one block north onto Riverside Avenue , now known as 4th Street .
US followed Riverside Avenue west and onto a curvy section near the confluence of the Big Sioux and Missouri rivers .
US 20 turned east onto 5th Street and US 77 turned west one block north onto Riverside Avenue , now known as 4th Street .