California Highway Patrol press release: 

On January 23, 2017, at approximately 11:05 AM, a  Ford pickup, driven by 58 year old Garberville resident Gerald Stillwell, was traveling southbound on US-101, north of Black Oak Ranch, near milepost marker 75.5, in Mendocino County.  For reasons under investigation, the Ford traveled across the center line of US-101, and collided head-on with a northbound Volvo semi-truck, driven by 63 year old Fair Oaks resident Gary Fischer.  The collision caused damage to the semi-truck’s saddle mounted fuel tanks, resulting in approximately 75 gallons of diesel fuel to leak onto the roadway.  A small amount of diesel spread to the west dirt shoulder of US-101.

Cal-Trans, Cal-Fire, Mendocino County Environmental Health, and Laytonville Volunteer Fire responded and assisted at the scene.
US-101 was closed in both directions for approximately two and one half  hours, for cleanup of the scene. 

During the investigation, it was determined that Stillwell was driving under the influence at the time of the collision.  Stillwell was arrested for suspicion of driving under the influence and booked into the Mendocino County Jail.

This collision remains under investigation by the California Highway Patrol.

PREVIOUSLY: Big Rig Collision Closes Highway 101 in Northern Mendo