SR-122 begins at the east right-of-way line of the Utah Railway, opposite the coal mine and ghost town of Hiawatha in the Manti-La Sal National Forest.

It heads east in generally straight lines, gradually descending a ridge from the foothills of Gentry Mountain into the Castle Valley.

About two-thirds of the way to the end at SR-10, SR-122 meets a county road from Wattis, another former mining town.

[6] Another branch, running southeast from Wattis to SR-122, became State Route 50 in 1935[7] and was also deleted in 1969.

[8] A short truncation was made to SR-122 at its west end in 1993, after Hiawatha was disincorporated, so that the U.S. Fuel Company could gate the former Main Street.