High Quality Content by WIKIPEDIA articles! State Road 120 (NM 120) is a 119.031-mile (191.562 km) long state road in the U.S. state of New Mexico. The route traverses four counties: Colfax, Mora, Harding, and Union, and is the longest state road in New Mexico. The highway`s only grade-separated interchange is with Interstate 25 in Wagon Mound.