Highway 101 over Cosi Hill will close to all traffic around-the-clock from 6 a.m. Monday, June 17 to 6 p.m. Friday, June 21, weather permitting, according to the state Department of Transportation.

During the closure, traffic will be detoured via State Route 107 and Blue Slough Road.

The five-day closure allows contractor crews from Rognlin’s Inc. to construct temporary lanes around a slide-prone section of the highway near milepost 78 in preparation for a 2-year construction project to stabilize the slide-prone section of 101. When the roadway reopens after June 21, travelers will encounter narrowed and shifted lanes through the work zone.

During the closure, travelers will follow a signed, 7.5-mile detour via State Route 107 and Blue Slough Road. The intersection of State Route 107 to northbound Highway 101 will close to traffic. Northbound Highway 101 drivers will detour using State Route 107. Southbound Highway 101 drivers coming from Aberdeen will detour using Blue Slough Road. Access to and from the Highlands Golf Course entrance will be maintained.

Construction to stabilize the hillside involves the digging of nearly 600 30- to 60-foot deep shafts and filling them with just under 29,000 tons of rock, according to project managers. Construction is expected to last into the fall of 2020.

Meanwhile, the Chehalis River bridge just south of Montesano is reduced to one lane as the bridge timbers are replaced on the south approach, modern safety rails are installed and the steel structure is painted. Backups can be expected through the area as traffic is controlled by a signal on each end of the bridge throughout construction, expected to last into the winter of 2020.