It is the only California state highway with an unpaved segment, which is a one-lane jeep trail on the northwestern face of the San Bernardino Mountains directly east of Summit Valley and northwest of Blue Jay.

The road briefly turns north further into the Hesperia city limits, leaving the San Bernardino National Forest.

SR 173 leaves the city and enters Mojave River Forks Regional Park, where it turns east and intersects Arrowhead Lake Road, which leads to the urban center of Hesperia.

[2] While roadway preservation maintenance (basic grading, debris clearance) is still done, this decision effectively ends all further interest to upgrade the segment to a 2-lane passable highway through state-funded projects.

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, based on the alignment that existed at the time, and do not necessarily reflect current mileage.