Classified as a rural major collector, it crosses Spring Glen Creek as it heads north toward its northern terminus at SR-157, spanning a distance of 1.4 miles (2.3 km).

[2] In 1969, SR-139 was extended east past US-6 and north through Spring Glen to meet State Route 157, eight years after SR-157 had been extended north from Spring Glen to Helper.

[2][3] The route was significantly shortened in 1975, with the 13.3 miles (21.4 km) west of US-6 being deleted from the state highway system, leaving SR-139 as a short connector between US-6 and SR-157.

[2] In 1978, SR-139 was lengthened by 0.1 miles (0.16 km) when reconstruction of US-6 in the area necessitated moving its intersection with SR-139 southward, resulting in the current alignment.

[2] The entire route is in Spring Glen, Carbon County.