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.The section of Route 128 through Navarro River Redwoods State Park is often closed in winter storms due to flooding.Even earlier, the road followed the Navarro Ridge, to the north of the present alignment, instead of staying at the river level.[7] By 1938, the last stretches of old winding roadway near the present location of Navarro were replaced by a straighter alignment, taken over from a disused logging railway line.[9] 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.
Highway marker showing cosign of US 101 and California Route 128