State Route 108 begins in downtown
Modesto at the junction of
SR 99 and
SR 132,
overlapping SR 132 northeast on L Street from 6th Street to 9th Street. There, it splits into a short
one-way pair, with eastbound SR 108 turning southeast with SR 132 on 9th Street to K Street and then northeast to Needham Street; the westbound direction remains on L Street to Needham Street. After several blocks eastward on Needham Street, SR 108 reaches McHenry Avenue, which it follows north out of the city. There are no route markers eastbound indicating where the route turns left from 9th Street to K Street, nor are there route markers indicating where the westbound traffic turns left from Needham Street to L Street. From Modesto, SR 108 runs north along McHenry Avenue for about before turning eastward on Patterson Road to follow the
Stanislaus River east-northeast. In
Riverbank,
County Route J7 comes from the north and departs to the south after about a one-mile (1.6 km) co-routing. After following the river about , SR 108 passes straight through the heart of downtown
Oakdale. At the main intersection in Oakdale,
SR 120 joins SR 108 from the north and they are co-signed as they continue northeast, climbing into the foothills and passing just south of
Knights Ferry. SR 120 brings with it the title
Northern Yosemite Highway for this segment; with
State Route 140 being the middle route from the west and
State Route 41 being the southern route to
Yosemite. Just past Knights Ferry, SR 108 crosses from
Stanislaus County into
Tuolumne County, and the road changes from two lanes to four-lane separated highway for about . This is advantageous as steep grade is located along this stretch of the road and the extra lanes are useful as passing lanes both ascending and descending the mountain range. About a mile after the end of the separated pavement,
La Grange Road (County road J59) heads south, passing just west of
Lake Don Pedro and meeting SR 132 near the town of
La Grange. Another eastward, at Yosemite Junction, SR 120 finally separates from SR 108 and heads southward toward to a co-routing with
State Route 49 through
Chinese Camp and across the upper end of Lake Don Pedro. Another eastward, SR 49 joins from the south and is co-routed with SR 108 through
Jamestown and into
Sonora, where SR 49 departs to the north. SR 108 continues eastward and gains elevation as it passes through
Twain Harte,
Mi-Wuk Village, Long Barn, Cold Springs, Strawberry-
Pinecrest Lake and
Dodge Ridge Ski Area, then on to
Dardanelle and Kennedy Meadow. SR 108 passes through
Alpine County for approximately 0.8 miles immediately west of the
Sonora Pass. At the pass, the highway crosses the summit of the
Sierra Nevada and enters
Mono County, then descends past the
Mountain Warfare Training Center at Pickel Meadows, finally reaching the eastern terminus at Sonora Junction where it meets
U.S. Route 395. Sonora Pass usually closes during the winter months, often from November through as late as May. SR 108 is part of the
California Freeway and Expressway System, and west of the eastern junction with SR 49 is part of the
National Highway System, a network of highways that are considered essential to the country's economy, defense, and mobility by the
Federal Highway Administration. SR 108 is eligible to be included in the
State Scenic Highway System, but it is not officially designated as a scenic highway by the
California Department of Transportation. ==Major intersections==