California State Highway 138

State Route 138
Map of southern California with SR 138 highlighted in red
Route information
Defined by
Maintained by Caltrans
Length:	105.376 mi (169.586 km) SR 138 is broken into pieces, and the length does not reflect the SR 14 overlap that would be required to make the route continuous.
Existed:	1934 – present
Major junctions
West end:	I-5 near Gorman
	SR 14 in Palmdale SR 2 near Wrightwood I-15 near Cajon Pass
East end:	SR 18 near Crestline
Location
Counties:	Los Angeles, San Bernardino
Highway system
State highways in California Interstate U.S. State Pre-1964 History Unconstructed Deleted Freeway Scenic ← SR 137 SR 139 →

State Route 138 (SR 138) is an east–west state highway generally following the northern foothills of the San Gabriel Mountains and the western Mojave Desert of southern California.

The scenic highway begins in the west at its junction with Interstate 5 located south of Gorman in the Sierra Pelona Mountains, continues eastward through the Antelope Valley and Cajon Pass, to its junction with State Route 18 in the east, located in the San Bernardino Mountains south of Crestline.

Except for the western two miles (3 km) of the route between Interstate 5 and just east of Gorman Post Road and a segment shared with State Route 14 between Avenue D in Lancaster and Palmdale Boulevard in Palmdale, it is all a mostly undivided two-lane surface road. The remaining section of the Ridge Route, California's first highway connecting the San Joaquin Valley to the Los Angeles Basin, ends at Route 138 near Gorman.

The western leg of State Route 138 traverses the Lancaster Freeway from Interstate 5 to Gorman Post Road, Lancaster Road from Gorman Post Road to 245th Street West near Neenach School, and Avenue D from 245th Street West to Route 138's north junction with State Route 14. The Lancaster Freeway has four lanes, two for each direction of travel. Both Lancaster Road and Avenue D are 2-lane conventional roads; Avenue D is on a straight alignment over its 22 miles (35 km) between 245th Street West and State Route 14.