This road, designated State Route 12 proceeded southerly from U.S. Route 91 (US 91) (now I-15) through Logandale and Overton and southeasterly to the former town of St. Thomas a total distance of  and then easterly crossing the Virgin River towards the Arizona state line over a distance of . The portion between US 91 and Logandale was paved by 1935, with pavement reaching Overton the next year.
State Route 12 started at U.S. Route 91 (now I-15), moving south through Logandale and Overton to St. Thomas, a total distance of , then eastward across the Virgin River towards Arizona's border over a distance of . The section from US 91 to Logandale was paved by 1935, with pavement reaching Overton the following year.