Route 128 begins at
Route 1 near the mouth of the
Navarro River at the
Pacific Ocean. The highway travels southeast and upriver, through the
coast redwood forests of
Navarro River Redwoods State Park and through the vineyards and apple orchards of the
Anderson Valley, to
Boonville.
Route 253, from
Ukiah, has its western terminus into Route 128 at the south end of Boonville. Leaving Boonville, Route 128 climbs out of the Navarro River watershed and crosses the Yorkville Highlands before descending into the
Russian River watershed, arriving at
Cloverdale in the
Alexander Valley, where the highway joins
U.S. Route 101 heading south. A few miles later, at
Geyserville, Route 128 separates from U.S. 101 and continues southeast through
Knights Valley on the way to
Napa Valley, where it joins
Route 29 at
Calistoga. After passing through the town of
St. Helena, Route 128 splits from Route 29 at
Rutherford and climbs east over dry ridges above
Lake Berryessa to the
Sacramento Valley. In
Winters, the route's constructed portion ends at
Interstate 505. By its legal definition, the route continues east along Road 93A and Covell Blvd to
Route 113 at
Davis and then Mace Blvd to
Interstate 80, but this segment is currently not constructed. The section of Route 128 through Navarro River Redwoods State Park is often closed in winter storms due to flooding. Two slower alternate routes are available: the Philo-Greenwood road connects Route 1 near
Elk to Route 128 near
Hendy Woods State Park, a few miles north of
Philo; another alternate route is the Comptche-Ukiah Road, which intersects Route 1 just south of the town of
Mendocino and runs inland to
Comptche, and departs Comptche on Flynn Creek Road, intersecting Route 128 just up river from the seasonal flood gate closing the highway. SR 128 is part of the
California Freeway and Expressway System, although it is mostly 2 lanes, but except for a small portion in Winters is not 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. ==History==