Proceeding west to east for 123 miles (nearly 200 km), the highway starts south of Panguitch at an intersection with US-89, crosses part of Dixie National Forest and Bryce Canyon National Park, continues through the small towns of Tropic, Cannonville, and Henrieville.

It then proceeds north through more of GS-ENM, Boulder, the Aquarius Plateau, and Grover, ending in Torrey at an intersection with SR-24, five miles (8 km) west of Capitol Reef National Park.

[3] The Average Daily Traffic (AADT) on SR-12 is at its greatest at its western junction with US-89, where the count for 2005 was 2,430.

That same year, a new State Route 120 was created, continuing the road from Tropic to Henrieville,[8] and in 1935 it became part of SR-54.

[11] An extension took SR-23 northeast to Boulder in 1941,[12] and in 1947 SR-54 absorbed SR-23, with the Widtsoe-Escalante road dropped in favor of Henrieville-Escalante.