SR 120 heads east along Elm Street until it crosses the West Branch Ellis River where it then heads southeast briefly paralleling the river.

Before reaching Ellis Pond, SR 120 makes a sharp turn to the southeast onto Roxbury Notch Road where it travels around the southern base of Partridge Peak at Roxbury Notch.

Descending from here, it begins to closely parallel the Swift River.

It continues south winding its way alongside the river through the town of Mexico before entering Rumford.

Passing Mountain Valley High School, SR 120 enters a residential neighborhood of the city where it travels along Hancock Street.