State Route 173 (SR 173) is a state highway in the U.S. state of California that runs entirely in San Bernardino County, mostly in the San Bernardino National Forest. Its west end is at State Route 138 near the west end of Silverwood Lake in the Summit Valley south of Hesperia. Its east end is at State Route 18 south of Lake Arrowhead. The route starts at the Mojave River Forks, skims the easterly and southerly sides of Lake Arrowhead and meets State Route 189, Lake's Edge Road, at the south entrance to the Lake Arrowhead Village. 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. Since March 2011, this one-lane unpaved segment of SR 173 has been closed. Through traffic should use SR 138 and SR 18. An alternate route from Hesperia to Lake Arrowhead would involve heading south on I-15, then south on I-215, then east on SR 210 in San Bernardino to reach the southern terminus of SR 18 at Waterman Road. From Wikipedia
